Opening editor is as hard as breathing, just select singleplayer tab and then click on "editor
"https://steamuserimages-a.akamaihd.net/ugc/1754687857180759062/7FDE1B1B0A89CBC6A6EE84A6E89DAA5886F2700F/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false
You will be asked to select map, it doesn't matter which one you select.
https://steamuserimages-a.akamaihd.net/ugc/1754687857180763494/B97E145B6BEACCCF9FBD8C2E46474D99F98CD203/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Select "men" category from big tab on the right an select an place some troopers
then hold left mouse button and select them all. After that right click on one of them and select "Save custom compsition"
https://steamuserimages-a.akamaihd.net/ugc/1754687857180797216/2D092CD5E73BF44C18FF6FB2D319B764602A1712/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false
After naming it and saving click F2 and go to the last tab
https://steamuserimages-a.akamaihd.net/ugc/1754687857180809380/0C2DDFB32A063E382989F923B3E0E076C6A996A2/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false
select your composition and in the bottom right corner above play button click little steam logo.
Add title, set visibility and agree to the Steam workshop agreement, then select publish.
There you go, after a while when project uploads you will get an achievement. immediately after finishingsteam workshop page will pop-up so if you want you can delete your composition from workshop.