Go into a public playlist, preferably TDM (you can change gametype) because there are more players in TDM
Then press F4 to set up the game and F5 whenever you wanna start. Noone will join in the lobby, you need to start the game in order to make people join you.
And if no one joins, go portforward or buy 10 new routers and try them all to see if they work.