I bet 100 tc to my friend, my friend won but i gained my 100 TC s back!?

The betting system works like this.
You do not bet against the system, there are no set odds.
Instead you get your winnings from OTHER people's bets. It's meant to be a gamble. In other words, how much you win is entirely based on how many people bet against the guy you're betting on. So if absolutely nobody bets against you, you make no money.
If you want to try and turn a profit betting, look out for betting servers hosted by staff. There are plenty of them around. Here you will be certain to find people who will bet against you, and if you bet on the right guys you can take their TC!
You can only win 5x as much as you bet, and how much you win is based on how large an amount of tc you bet. In other words a 1000 tc bet will win more than a 100 tc bet.