If you're offered bail, it means the legal system says you're safe to leave jail wile awaiting trial (people considered dangerous aren't offered to leave jail on bail).

Rich people can always afford bail, so they get to live normally while preparing for trial. Poor and middle class people often can't afford to pay bail, so they're stuck in jail, unable to pay the ransom fee. The bail fund is a way of allowing poor and middle class people to go home to their families and jobs while preparing for trial (the way rich folks are able to).