to invite your people you must meet them in a match like matchmaking. then after you met them you go to your friend list. and u go to recent players. there you can invite them to your game or become friends with them. in order to invite your friends you must have an open party, and there has to be room for the person too. people cannot join you if you are in a matchmaking match. you must be in the lobby, but that's not for custom games. in custom games they can join whenever they want. but the party must be open.