When a person has been arrested for a violation of the California Penal or Vehicle Code, they will be asked to appear before the Judge on set date. That date is the date of their arraignment. The arraignment is when a person enters a plea with the Judge. They may plea guilty, not guilty, or no contest.
At the arraignment the Prosecutor will also give you an offer. The offer is a plea bargain that will give you the potential sentence they can offer you, if you agree to plead guilty and not try the case. It is important to note that it is your constitutional right to have a trial, where the evidence may be presented and the ultimate verdict determined by a jury of your peers.
If you choose to take the offer given by the Prosecutor and plead guilty, you are waiving your right to a trial and to be heard. This is a very important decision and must be understood completely before any kind of offer is accepted.