What will be my penalty if I’ve been charged formisdemeanor vandalism?

You can ask for a court appointed attorney when you appear  in court, however you must be income eligible. If you can't get one appointed to you, you should seriously consider getting a private attorney. In CA,  if you are convicted of defacing property with "graffiti or other inscribed material", the cost of the damage is less than $250, and it is your first vandalism conviction, a prosecutors may opt to charge you with an infraction under Penal Code 640.5 or 640.6 PC. An infraction subjects you to a maximum $1,000 fine and community service, plus this is not considered to be a criminal offense. An attorney can be instrumental in getting the state to accept the lesser offense.

If however you are convicted of misdemeanor vandalism under Penal Code 594 PC, you face informal (otherwise known as "summary") probation, up to 1 year in a county jail, a maximum fine of $1,000 (or up to $5,000 if you have a prior vandalism conviction), a driver’s license suspension of up to 2 years, counseling services, and community service, or personally cleaning, repairing, or replacing the damaged property, or keeping the damaged property or another property in the community "graffiti free" for up to 1 year. However, if you are granted probation in a misdemeanor vandalism case, you may expunge your criminal record (i.e. have it removed) once you successfully complete your probation.