I have gained a lot of tc from betting, but sometimes it doesn't work. So i am asking when and where can you bet, and do other people have to bet too for you to win?

If you (or you + a few folks) bet on one guy, and nobody bets for the other one, there's no actual pot.
You can bet on every server, at first 50 frames of the battle, I guess...
Also, the minimum bet is 100 TC. I don't know, though, if it's like that due to some update or manually set by others.

If you bet 100 on a person, and another bets 100 on another one, then if him your betted on wins, will you get 90% of the tc's.

really? cuz when i bet 5000 on this uy and i won, i got 8000 tc back

Probably because there's other people that have betted on the same person ?

wait when you are the only one who bets, do you just get your money back? or do you get more?

You lose some money, some goes to the winner.

Eh, not really.
"A" bets on "B"
"B" wins "C"
"A" gets all his money back because no one bet against him.

However

"A" bets 100 TC on "B"
"C" bets 100 TC on "D"
"B" wins "D"
"B" gets 10 TC
"A" gets his original 100 TC + 90 TC which is what remains of what "C" bet.

I bet on one guy but he quit in the middle of a match and I didn't get it back.
It was only 100tc though.
[lelelelelel]