I just got hurt at work. What do I do?

Five steps, in order. The deadlines here are real — missing them can hurt or end your claim.

1. Get medical care first. If it's an emergency, go to the ER or call 911 — treatment comes before paperwork, always. Tell every medical provider that you were hurt at work, so it goes in the record and gets billed to workers' compensation instead of you or your health plan.
2. Report the injury to your employer — in writing, as soon as you can. California law expects notice within 30 days of the injury (Labor Code § 5400). Don't wait for the deadline: report it the same day if possible, to a supervisor or HR, and keep a copy or photo of what you sent. An injury that develops over time (back, joints, repetitive strain, hearing) counts too — the clock generally starts when you knew, or should have known, it was work-related.
   Reporting a work injury is your legal right. It is illegal for your employer to fire you or punish you for filing a workers' compensation claim (Labor Code § 132a).
3. Get the claim form (DWC-1) and turn it in. Within one working day after you report the injury, your employer must give or mail you a DWC-1 claim form (Labor Code § 5401). Fill out the employee section, keep a copy, and give it back to your employer. If they don't give you one, you can download it from the state Division of Workers' Compensation (dwc.ca.gov) — and their failure to provide it is worth mentioning to a lawyer.
4. Know what the insurer owes you while it decides. Once you file the DWC-1, the claims administrator must authorize medical treatment while the claim is under investigation, up to $10,000, even before accepting it (Labor Code § 5402(c)). If the claim isn't rejected within 90 days, it is presumed compensable (Labor Code § 5402(b)). "We haven't accepted your claim yet" is not a lawful reason to give you nothing.
5. Keep records of everything. Every visit, every form, every letter, every phone call (date, person, what was said), every mile you drive to appointments and every parking receipt — travel to treatment is reimbursable. A shoebox of receipts and a simple log can be worth real money later.