From what I have found you are unable to join factions in the mod and the recruiting thing is broken in the depots. Personally I decided to use cheats to join the faction of my choice and began playing the game as usual from there.

If you want to do the cheat route to join a faction, type cheatmenu into the command console. Then find the leader of your desired faction and open the conversation dialogue. Click "CHEAT: Take the following action" where there should be a following dialogue box that says something like "CHEAT: Join your faction" or "CHEAT: Let my join your faction".

Hope this helps. Cheers!

You join a faction by doing exactly what is written in the game. Talk to a recruiter in a capital city or the liaison in a depot.