How can you make servers that play for credit?

Only official servers give you credits for wins.
Self-made servers don't.

You can buy boosters, then every server will give you toricredits, the amount the booster worths, but if you dont have a booster, its like Odlov said: you cant get TC on user created servers.

thx ... how do you make a server private? is that possible?

Cant make it definitely private.
You can set the maxclients to 2 so only you and yourmate can play, but ingame moderators (guys who have ~) can join no matter what.

ok thx

You can set the Maxclients to min (4 or 2, I think it's 4 though), put a password (/passwd your password here) and type /pass the password to to enter your password, and well, that's all.