Bail is the amount you must deposit to be released from jail.
That can be done in many forms. Cash, stock, property, etc. If you post this kind of bail, after the trial, if you haven't fled, you get 100% of it back. If you flee, you lose it.
Most people are not in a position to post cash or even property bail. Hence the bail bondsman. For a fee of 10% of the bail amount, he will post his bond as your bail. At the end of the day, if you don't flee, he gets his bond back and keeps your 10% as his fee. If you flee, the state makes him pay the bond amount. And he'll be sending bounty hunters after you.