The simplest Unit you can create is a simple Sprite replacement where you use your own Sprite and the default animations.

Go into the Data/Textures folder and open the Default Sprite Sheet. Here you can draw your own Unit Body Parts and place them in the correct locations.



Once you have your Sprite Sheet created open the game and go into Build Unit.

Click 'New', Select your Sprite Sheet, give the Unit a name and hit 'Save'.
Your custom Unit has been created! Hurray!

Go into Sandbox mode and spawn your newly created Unit Type!



Congratulations!
You can now upload your basic unit to the Workshop where everyone can see!

If you want you can expand your Unit with your own AI and with your own Animations. Explore the menus and check out the other guides.

Cheers!