First, you must start the Object Manager (requires Java 1.6+). To do this, start the game and choose "Add Your Own!" from the menu.
The game will automatically close once the Object Manager opens. In the Object Manager, click "Add Object" in the left panel and you will see a bunch of editable properties appear in the right panel for the new object.
Enter a unique identifier for this object in the top field, and the object will be created. You can delete an object by selecting it and hitting the delete key, and you can edit an object by selecting the object you want to edit (and it's properties will appear in the right panel). For more information on editing all the properties, see the below sections.

Once you are done editing and creating objects, you can save the edits (Ctrl+S or File -> Save), and then re-open the game (F5 or File->Run ADventure Lib). Once ADventure Lib restarts, all saved objects will be instantly in game, but given the random nature of the shuffling, they might not appear every game (and who knows where they will appear in game!)

Once you have created an object, you'll want to edit the info for it. After selecting an object on the left, you can edit the information in the Info Tab.

• Identifier - A unique identifier for the object. This is not visible in game, but is used to keep track of which object is which. If two objects have the same identifier, then one of them will not be loaded in game. The object manager will not let you create two objects with the same identifier, but this is possible if you subscribe to workshop items with the same identifier, so try to keep your identifiers unique. There can be two objects named Chicken in game, but they can't both have the same identifier of "chicken."
  
• Name (ex: Banana) - The name of the object, as it appears in game. The case of the name does matter - this is exactly how name will appear after a period or if the "has lower case" property (see below) is not checked.
  
• Name Voice - The above name, voice acted. You can record directly in the Object Manager using the record button, or you can import .wav, .mp3 or .ogg files (recorded by any software) by hitting the browse button. If added, then this voice clip will be played whenever the object is spoken of in game. I recommend having little to no silence/extra space in the clip so that the sentences sound continuous - but the Object Manager will automatically attempt to trim the silence if you use the built in record button.
  
• Has Plural - Whether this object's name has a plural form. Most words have a plural form, but some do not (like Butter). You should only uncheck this if the name is the same whether it is singular or plural.
  
• Name Plural (ex: Bananas) - The plural form of this object's name, as it appears in game (the same case rules as the Name applies). Usually, this is just adding on an 's', but some words have pretty weird plural forms (like Cacti). You might need to get creative for some objects. Like, if I wanted to add myself (David), I could set "Davids" as the plural form, but that's a little strange. I could also use "People" or "Men" as a more generic way of referring to a lot of people named David.
  
• Name Plural Voice - Exactly the same as Name Voice, except for the above plural form.
  
• Has Indefinite Articles - Whether the name can have indefinite articles (a, an). Most words can, but some words (like Butter again... "a butter" just sounds weird) don't.
  
• Name Indefinite - This displays the name, with "a" or "an" before it if indefinite articles are allowed. This is automatically generated based on whether the name starts with a vowel or not, and cannot be edited.
  
• Name Indefinite Voice - Exactly the same as Name Voice, except for the above indefinite form.
  
• Has Lower Case - If checked, then all the above names will be made lower case when not immediately after a period. Usually, this is what you want, as it is weird to have lots of capital letters everywhere. However, for proper nouns (like David), I might want the D to always be capitalized, so then I would uncheck this to ensure that David is always written with the case I used in the name field.

Don't forget to save your object if you are done editing it (Ctrl+S or File -> Save). Unsaved changes will be lost when you close the Object Manager.

Unless you want the object to be completely invisible in game, you'll want to click the Image tab at the top of the Object Manager and draw (or import) a graphic for the object. The image must always be left facing (you can use your best judgement for objects where it's unclear what "facing" means). Yes, this means if the object is selected as player, this exact image will waddle about, flipped over the x axis if the player is walking right instead of left!
The drawing app is pretty standard, with a minimal feature set (but it includes pressure sensitivity for those of you lucky enough to have a drawing tablet). The controls at the bottom are:

• Zoom - Zoom the canvas in and out.
  
• Color - The current drawing color. When clicked, a popup will appear that lets you change the color. This popup can be left open to quickly change colors. At the bottom of the popup, there's a "Pick a Color" button that, when clicked, will let you pick a color from the image.
  
• Opacity - How opaque the brush is.
  
• Brush - The type of the brush. This can be Point (a circular brush type), Bristle (a rougher brush type that looks like it has bristles), and Eraser (erases instead of draws, with a circular brush type). If you have a tablet, you can use the eraser end of your pen to erase without changing the brush type.
  
• Brush Size - The size of the brush, in pixels.
  
• Softness - How soft the brush is. Low percents give harder edges, and high percents give softer edges.

Below the controls, there are three buttons:

• Browse - Import a .gif, .png or .jpg image. Useful if you'd prefer drawing in photoshop or gimp. The image should be 256x256px, but it will automatically scale the image if it is larger or smaller.
  
• Flip X - Flips the image about the x axis. Useful when trying to figure out which direction is actually left facing...
  
• Outline - You might have noticed that in game, all the objects have a slight black outline around them. This button will add a black outline, which is nice because it makes the object easier to see on bright backgrounds and makes it more consistent with other objects in game (but it's completely optional).

Also note that ctrl-z will undo drawing actions, and ctrl-y will redo them.

Don't forget to save your object if you are done editing it (Ctrl+S or File -> Save). Unsaved changes will be lost when you close the Object Manager.

Once you've added an object, you might want to share it with others by uploading it via Steam Workshop. You can do this by clicking File -> Share via Steam Workshop, which will bring up the following popup:
This popup includes current identifier and image for your reference, and then asks you to add a description and a change note (optional). The description is what will appear in the description section in the Steam Workshop, and can be edited later. Once you're ready, just click share. ADventure Lib will then open to share the object - this is not a bug - do not close the game until the object manager shows a popup that says the sharing was complete (or it might give you an error message if there was an error).

Once the sharing is complete, it will open it in your browser and you can then make it publicly visible, or share only with your friends. The object manager always uploads new objects with private visibility. If it does not open automatically (I noticed this happens in Linux), then you can go to your content in Steam and click Workshop to view all your uploaded workshop items.

If you edit the info or image of an object, you can update it by clicking File -> Share via Steam Workshop again, which will bring up the same dialog except with the share button replaced by "Edit." You can then update the description and add a new note for the changes you have made, if desired. Change notes are useful to add for edits, so that people who have subscribed to your object can know what changed.