You shouldn't just walk into court and plead guilty without speaking to a lawyer. In fact, if you're charged with a felony, the judge will not allow you to do it unless you specifically waive your right to a lawyer and make a motion to represent yourself.
If you can't afford to hire an attorney, ask the judge to appoint the public defender to represent you. Public defenders are attorneys paid by the government to represent people who can't afford to hire their own attorneys.
It is impossible to give you meaningful advice on how to handle this case without reviewing all of the relevant information. Your attorney will have access to all of the police reports after your first appearance.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like Avvo, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
Don't make another HUGE mistake by just walking in and pleading guilty.
If you cannot afford an attorney, the court will appoint the public defender to represent you. You need an attorney to review the case and see if you have any defenses or if there can be anything worked out to minimize the impact on your record, future and freedom.
Please do not just go in and plead guilty. I am a defense attorney in San Diego and can assure you that this is not your best option. If you cannot afford a lawyer, and I suggest you at least talk to one because many of us work with payment plans, you can have the court appoint a public defender to represent you. No matter who your lawyer, they will be able to sit down the prosecutor at a future court date and work out a much better deal than you would get by just walking and pleading guilty, and pleading not guilty at that first appearance will not hurt you at all! Who knows, maybe after looking at the evidence there will be enough to get you off completely ;)