Placing a bet is done by clicking on the field of the respective colour. The amount of the bet is determined by which chip is selected. You can place a bet on all sectors.
Next to the amount of chips in your wallet, you will see two buttons - the first becomes active when your chips fall below the starting amount you logged in and allows you to add additional chips in your wallet to reach the same number you logged in. By pressing the second button, you will repeat your bet from the previous spin of the wheel.