Its generally just a cash or money order service. If you need to get someone out of jail, you just call one, they already have the records or access to them at their finger tips, and they can tell you how much it'll take from you for them to cover the rest in good faith the person getting out of jail will appear at their court date.
It mostly depends on the situation. Generally, you just call a bail bonds and tell them who you would like to bond out. Most bail bonds will require collateral and full premium payment up front, how ever some like mine will offer easy payments and no collateral. For more information visit bail-bondssacramento.com