Hello everyone, I was looking for a tutorial to create a worldspawn for a predominantly black sky, where you could also create small dark corners or other ...
Someone more experienced than I know how to do?

Make backups of your .map before adjusting skybox kvp. Bad values can crash radiant.
//
Sky textures emit light. Pick a dark one to start. Change the sky texture in radiant, change the worldspawn skybox kvp. Add xmodel,skybox to your zone_source/mapname_patch.csv if you have one.
Reduce "sunLight" kvp
Reduce "sunRadiosity" kvp
Use lower intensity values than 1 on lights. Dont use any "primary omni" lights.
Use caulk shadow.
You could also make a black skybox and add the stars or cloud meshes from another skybox.

Here you can see some skyboxes to pick for the map:
http://wiki.modsrepository.com/index.php?title=Call_of_Duty_5:_Skybox
Actual settings to replicate the map in question, you can google them all if unsure what it will look like before trying any:
http://wiki.modsrepository.com/index.php?title=Call_of_Duty_5:_Worldspawn_Settings