To back a selection is to place a bet for something to happen.
For example to back Manchester United would be to place money on them to win their match.
If they win, so does your bet. It’s just like the bet you’d regularly place with a traditional bookmaker.
I am backing Bayern Munich 1dBTC at odd 3.00.
This means that if Bayern Munich wins, my bet will be a winner and my payout will be 3x1dBTC = 3dBTC.
If Bayern Munich doesn't win ( CSKA or DRAW) my bet will be a loser and I'll lose my 1 dBTC.
Check Image Below.