How do you report hours that vary week to week? - 2 months and counting

I picked up part-time shifts as a security officer and I am confused about how to report them. It has been weighing on me all week. The form asks for gross earnings, which I do not see until later. Who can I ask without risking my claim?

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.