Read What to Do After the Court Decides Your Small Claims Case (Form SC-200-INFO).
If you did not go to the trial for a good reason, you can ask the court to vacate (cancel) your judgment (called a "default judgment") and give you a new trial date. You will need to file a form called Notice of Motion to Vacate Judgment and Declaration (Small Claims) (Form SC-135).
If you lost and owe money, pay the court or the other side (the plaintiff). If you do not pay, you must mail a form called Judgment Debtor's Statement of Assets (Small Claims) (Form SC-133) to the plaintiff within 30 days. After you pay, make sure the plaintiff files a form called Acknowledgment of Satisfaction of Judgment (Form SC-290 or Form EJ-100). If the plaintiff does not file this form, you can ask the court clerk to enter a "satisfaction of judgment" if you can prove you paid the full amount of the judgment with the interest and costs.
If you won after filing a Defendant's Claim and the other side owes you money, try to get them to pay you. Once they have paid, file an Acknowledgment of Satisfaction of Judgment (Form SC-290 or Form EJ-100).