First step.
Prepare a new text file on your windows desktop, give it a name: "new map.txt".
Open it and write in few words a description of your new map. Do not use diacritical fonts used only in your language (for example: "ą, ę, ź, Ü, etc.).
Save the file.

Second step:
Download and save on your desktop this picture.
You will need it to use as temporary tumb picture for your new map.
https://sp.zhabite.com/sharedfiles/filedetails/?id=1835578385

Next step:
Run the game and in the menu click as shown in yellow elipse:
https://sp.zhabite.com/sharedfiles/filedetails/?id=1835573445

Now you are here
Click the cross in red elipse
https://sp.zhabite.com/sharedfiles/filedetails/?id=1835574148

So, then next steps are marked by numbers.
1 - give a name for your map
2 - choose a type of project - make sure it is Landscape It is Important!
3 - click it and choose the file you created at the beginning, this one with map description
4 - click it and choose the file with downloaded tumb picture
5 - click ːsteamhappyː

https://sp.zhabite.com/sharedfiles/filedetails/?id=1835574749

Now you can enter into map editor by click on the "net" icon:
https://sp.zhabite.com/sharedfiles/filedetails/?id=1835575208

Icon next to it with green "V" is used to sending the map to the Steam's Workshop when it is finished and ready to share with players.

Goodl luck, Comrades.


Edit.
In addition:
https://sp.zhabite.com/sharedfiles/filedetails/?id=1835594235