To bet just click on the points under the columns 1 / x / 2.
To bet for the bonus points in the knockout phases, click on the dot next to the team you think is going to qualify.
Under column B you can find the bonus points you can win.
Save by pressing "SAVE BETS!". (duh)

To bet for the Competition Winner Bet, select the team of your choice and click "SET!". (duh)
You can’t change your choice after the cup has started, as the bet will lock two hours before the first match of the competition.

Also don't forget to check here under betting.