Personally I bought this game without much background knowledge with farming or the series, so when I got into it I found that there were no guides that explained basics or things that I personally found confusing at first in detail. So after devoting some hours and getting everything cleared up myself, I decided to write this to help out anyone who may be in my situation when I first bought the game.

Managing your finances in Farming Simulator 2015 is quite important. While it is easy to make a good income in this game, you can easily save thousands by considering the finances which would be loan interest, maintance costs, income from placeables, worker wage, etc. Whenever you have a loan you are constantly paying loan interest, it costs money to borrow money. Unfortunately the loan interest doesnt seem to be displayed in the PDA (press I to access it) but is displayed in the ATM station (Dollar symbol on the minimap, press 9 to access minimap). So if you want to check how much money you're losing exactly you should pay a visit to one of the ATMs. Also to note is that you should pay a lot of attention in the store as to what the maintance costs are and what some of the passive profits are, some things are hourly and some are daily. Personally I'd recommend calculating everything hourly to a daily income/expense just to make it easy. For example a beehive makes $30 an hour so $30 x 24 hours would make it $720 a day. Personally I always try to get rid of the loan as soon as possible, as the quicker its gone the more money you save from loan interest. Also note that the starting tractors have a horrifying $460 daily maintance cost compared to the other tractor's $200-300 daily maintance.

The game has a basic supply and demand economy system in it. All the places you can sell your products at (Grain mill, transportation company, etc) are competing with each other for your goods, so one place might offer a "Great demand" or pay a considerably larger amount for something. These great demands are brief however and most of the time it'll end too quickly for you to grow something. Considering this you should consider whether to store your grain or sell it for normal prices. If you sell a lot of wheat for example, to the grain mill the price will drop significantly, however if you don't sell any wheat for a long time the price will rise. You should also check to see who's paying the most to buy your grain. While it is typically a good idea to always sell to that one place always paying the most for it, it'll unlikely ever have a great demand due to it being constantly supplied by you. Knowing this if you want a huge profit you can try to sell your grain to the lesser selling places and wait for the place selling the most to reach a great demand. If you're a starting farm though, it's probably best to just sell the grain right away then wait, as you'll typically need the money then than later.

There are a few buttons not explained by the game tutorial or often known by many people, here is a list of some of those controls discovered by me and mostly my friend Valkyra.

Cruise control: 3 - By activating cruise control it holds the machine at a certain speed for you, so you don't have to hold the "W" key down constantly.

Cruise control adjustment: 1 and 2 - These buttons control how fast you want the machine on cruise control, one lowering the speed by one unit, and two increasing it by one unit.

Blinkers: (Numpad) 1, 2, and 3 - These buttons toggle the blinkers on machinery that has them, one turns on the left blinker indicating a left turn, and two turns on both blinkers to indicate a hazard warning, three turns on the right blinker to indicate a right turn. These buttons are mostly useful for multiplayer as the AI doesnt respond to these.

Beacon: Home button - This button activates the beacon featured on some machinery, the beacon is the yellow light on the roof that flashes. Featured on all harvesters, it's mainly used to signal something, the AI uses it when the storage is almost full in harvesters. Again this is mostly for multiplayer as the AI does not respond to this.

Lights: F - This button toggles the lights on a machine, some feature rear lights so pressing the button twice activates them as well.

For those unsure with what's more efficient for your fields, this section will explain. The game works with a series of stages in working on your fields, cultivating, sowing, fertilizing, and harvesting.

Cultivating: Cultivating the fields is where you take a cultivator or a plow to "clean up" any existing plants on the field and to organize the dirt into rows for seeding. Using a cultivator or plow has no difference in yield efficiency, so it's best to just save the plow for expanding or connecting fields.

Sowing: Sowing is where you plant the seeds of your choice into a field. A variety of crops can be sowed into a field such as wheat, barley, canola, corn, sugar beats, and potatoes. Becareful when sowing grass, as it removes the plowed dirt, if you want to grow wheat again you have to replow the affected land. Grass does not remove plowed land if it has crops already sowed on it. Note that some equipment can cultivate and sow at the same time, pay attention to item descriptions.

Fertilizing: Fertilizing is very important, as it doubles the yield instantly. Almost all agree that buying a fertilizer should be your first and most important purchase. You can fertilize a field by using a sprayer, a spreader, slurry tank, manure, etc. All these methods of fertilization have equal yield efficiency, but some are more cost effective. For example a sprayer uses its contents a lot less than a slurry tank, but is more expensive to refil.

Harvesting: Harvesting is when you gather up the crops after it has fully grown. Most of this is done by a harvester, but some require special attention. When growing sugar beat or potatoes, you have to remove the top first, which requires special equipment for that. With the Big X 1100 harvester and some headers, you can harvest corn and other crops into chaff. Chaff is basically plant matter chopped up which can be deposited in a silo which can then fermate into silage. Grass can also be fermated into silage.

Below is a field that was cultivated, sowed, and fertilized.

Silage can be a bit confusing to explain for people. To make silage you need grass/chaff deposited in a silo. The silo looks like two concrete blocks and a space inbetween the two, there are four of these featured in the biogas plant and one at the cow ranch.

A silage silo

You need to compress the grass/chaff in order for fermentation to begin, in order to do this you can use any machine to drive over it. You'll see a UI on the top left that says "Compression 0%-100%"

Note that in order for fermentation to happen, the silo needs to have at least 10% capacity filled.

You'll know that the fermentation has started when a white tarp covers the grass/chaff and the UI says "Fermating..0%-100%"

Once the chaff/grass has fermated (Takes about a day) the tarp will be taken off and the chaff/grass will turn into a darker green color.

You can sell the silage to the biogas plant by picking it up with a front loader using a universal bucket and dumping it at the two black containers, or you can feed it to your cows.

Black containers described, dump your silage here to sell it to the biogas plant.

Cows are the most profitable farm animal and take the most of your time. They require a large starting capital and aren't as hard to take care of as they may seem at first.

Quick few definitions of keyterms
Straw: The product your harvesters dump if you enable the straw swath, you can pick it up with a forage wagon.
Silage: Fermated grass/chaff
Hay: Dried up grass

Cows are a bit picky with their food, you need to feed them a certain mixture to reach 100% productivity. Dumping grass into the troughs will not reach 100% productivity, however, dumping some straw into the toughs and it will improve productivity and cows will start producing manure. Note that cows start producing slurry with or without food.

You can reach at most 80% productivity by dumping a mix of straw, silage, hay, and grass, but if you want to reach 100% productivity you need a mixer. To do this you'll need a frontloader which can be a tractor that can use frontloaders, a telehander, or a wheel loader with the proper attachments, and a mixing wagon. Unless you use the self propelled mixing wagon, you'll need bales of hay and straw to be able to pick up the product and drop into the mixing wagon. For silage you'll need a universal bucket to pick it up from the silo and dump into the mixing wagon. It's recommended to make a mixture of 25-50% hay and silage, and no more than 40% straw. You can check by going into the tractor with the mixer. Once you're full, you can dump this into the troughs and the cows will eat it, reaching 100% productivity.
Troughs described above

Hope this guide helped a good amount of whoever is reading, if you have any questions post them in the comment and I'll try to reply as soon as I can. Happy new year and good luck at the farm.