A Felony Arraignment in CA is the first court hearing where an accused goes to court (or is brought if in custody) to hear of the offenses being charges (what the alleged crimes are), and to enter a plea. The plea is either 1) Not Guilty, which means there is a pending investigation and more court dates that potentially leads to trial, or 2) Guilty, where the accused says they did the crime and receives the punishment (sentencing). In some instances, a Lawyer will Continue the Arraignment, meaning the accused will enter a plea at the next scheduled court date. Lastly, the arraignment is where an accused can ask for representation (a lawyer) if he or she cannot afford one.
With Felony cases, (Aside from PC1000/P36 drug cases) generally a plea is not entered at the arraignment, since the lawyer will want to look into the case and do some investigation, perhaps later plea bargaining with the DA.
Keep in mind that a Not Guilty Plea can always be changed later when the defendant wants to take a deal.
Lastly, the arraignment also confirms the identity of the accused, making sure they have the right person.
All that my colleague said is true but it should be added that in felony cases there are two arraignments. The first is an arraignment on a felony complaint. After that the prosecutor must demonstrate probable cause for the charge usually done in a preliminary hearing. If you are then held to answer an "information" will issue and you will be arraigned on that in felony court.
There is a third type of arraignment. If your case proceeds to a grand jury and an indictment is issued, you can be arraigned on the indictment. That process takes the place of a preliminary hearing as the probable cause hearing.