How do you add players to your clan?

I entered =ONI= into the TWL but I dont see how to add members to the team. Is that something they have to do themselves?

yes. They will need to register in the system. When you setup the team you chose a 'join password' you must give this to your team members. After they register they just need to go to your team page, which is accomplished by clicking the team name on the game ladder, or you can link them. From there they need to click 'Join Team' it will give a popup asking for password, once that is entered its good as gold.