Clearly no betting company would survive if it simply gave away free cash to everyone. So most sportsbooks have terms and conditions which state you have to bet a little before you can withdraw your funds. This is known as the wagering (or turnover) requirement.
So in Bovada’s case the wagering requirement is set at 5 times your initial deposit and bonus. Therefore if you make a $100 first deposit you will receive a $50 bonus making $150 which you will need to stake 5x (so $150 x 5 = $750) to complete the wagering. If this is too much for regular stakes then choose a lower amount for your first deposit.