In Worldbuilder, go to file -> Export Package. That'll make it playable on your copy of CoH2, but nobody else's. You can play custom skirmishes on it and make sure everything works.
To upload it to Steam, go to Workshop in the CoH2 menu screen, select your map and click 'Publish'. If you want to change it, just make changes in Worldbuilder, then export and publish it again - as long as the filename hasn't changed, it'll just update the old version.
I had already Export Package, but still I can't find the map when creating a skirmish. Tthe message of confirming saving when the WB Export Package says that it is saved in a different folder not related to the game in steam, so I coppied and pasted in the file C:\Program Files (x86)\Steam\SteamApps\common\Company of Heroes 2\CoH2\Data\Scenarios. That way one of the files should work, but that doesn't hapens.
Any thoughts about that? I appreciate your help