Legal Question in Civil Litigation in California

You would need to file a memorandum of points and authorities.

Sometimes, courts might weigh the issues on their own without a written opposition having been filed. But I wouldn't advise that, since it's almost a suicidal maneuver to not respond. There is no official form. You should go to the law library or find a memorandum of points and authorities in opposition to the demurrer online that matches your needs. Essentially, you have to show in writing why the facts you stated in your complaint are sufficient to move the lawsuit forward, and integrate case law and statutes in support of your argument.

You would need to file an opposition to demurrer. Since you don't know that, and don't know how to do that, I can pretty much guarantee that even if you somehow manage to survive the demurrer, you will lose the case unless you hire an attorney. In over twenty years of litigation, I have never once seen a person representing themselves win against an attorney. So unless you want to hire an attorney, I suggest you just let the demurrer be ruled against you.

As Mr. McCormick said, if the case is important to you, use an attorney. Either you can afford an attorney or you can afford to lose the case. One or the other.