Mostly on target so far.
When you are arrested, you are in the custody of the cop who arrested you. Until the charges are disposed of, you have to be in someone’s custody. That can be your own self. When the judge figures that you’ve lived in town for 60 years and are charged with disorderly conduct, you’re not likely to head for the Mexican border, so he releases you on your own recognizance – i.e., in your own custody.
A child under arrest might be released to his parents’ custody – they’re responsible for making sure he’s back in court.
You’re never committed to jail before being found guilty; you’re remanded to the sheriff’s custody. Since the sheriff runs the jail, he keeps you there. It’s within his rights to have you do whatever he feels safe to permit, e.g., run errands outside the jail facility, take you home to dinner with Aunt Bee, or whatever, but he’s responsible for you to the court, so he’s within his rights to lock you up.
With certain exceptions (e.g., premeditated murder, Unabombing), you’re always entitled to bail. It can be set extremely high for serious offenses, but it has to be at least a possibility.
In North Carolina, there’s something called “unsecured bail” – which apparently consists in you guaranteeing to pay the amount of your bail if you don’t show.
Bail bondsmen post your bail with the court. They charge you a nonrefundable fee, usually 10% of the bail, for doing so. A bond is simply the physical thing that guarantees the bail, such as a document in the proper form from the bail bondsman to the sheriff or court.
New York instituted a neat little twist to this whole thing – if you are released on bail, they keep 10% for processing costs when it comes time to refund your bail. I’d love to see this challenged in Federal court.