Hi there. So i just started a game and followed the other guy around the base for some training (tutorial) before some briefing. When i thought i had done all that was available (shot some dummies and "fought" against other soldiers, looted the warehouse and garbage bins, helped the sick soldier) i tried to find the entrance to the main buncker to attend to the briefing. Found an open door with a green transition area in the big building to the south of the camp and moved there. Then i found myself outside with some bandits who robbed me.

Where is the briefing? I see i have some quest added to the journal but how do i get to attend to the actual briefing and receive my mission?

Briefing is a movie you saw just after entering ATOM bunker and before being robed. Don't skip the movie and you'll get all info for the main quest.

EDIT : OK, i found it. There's an option "show cinematics" that for some reason (probably cause i accidentally clicked it) was unchecked which is why i wasn't seeing it.