Don't start working without an active contract, which would show in your "My Jobs" tab. You can find more details here. To qualify for Upwork Payment Protection, make sure Escrow is funded for a Milestone before starting any work if the job is Fixed price, or use the Team App, enter work-related memos and make sure the client's payment method is verified before working on Hourly jobs.
Let me also share a few other resources that you may need as a new freelancer on Upwork. You can find valuable information in the Getting Started as a Freelancer section of the Help Center. I also advise watching our educational videos and reading the best practice advice shared by other users:
To help you work safely on Upwork, please have a look at tips and warning signs shared in this thread.