You can complete some initial quests for each faction and then decide which suits you best. You don't have to take a decision right now. There are of course more Minor (or Other) Factions, but only these listed below count during the final battle for Hoover Dam: The other factions have their own specific plans for other groups and prefer that some of them are eliminated and some better join them. You are able to eliminate, ignore or try to side with any of factions but you have the greatest freedom in case of the Independent Vegas. You can choose one out of four possibilities:

Once is completed, a moment comes when you have to choose a faction you'll be loyal to.