When you are charged with an offence you will be, depending on the charge, placed on bail until your court date. This means you are released on the condition that you will appear in court at the specified time and date, to answer the charge(s). In this sense, bail is like a promise or a contract to come to the court and deal with your charge.
Should you not appear in court the Magistrate will take that you have breached bail. In this instance the Magistrate may place a warrant out for your arrest. This warrant will be forwarded to the Police who will then in turn seek to arrest you to bring you before the Magistrate. They do this by attending your home, place of employment, or if you are pulled over in your vehicle you may be taken in from there.
For more serious charges you may have terms included in your bail. This means along with agreeing to appear in court at the allocated time and date you may also have to do things such as: