What kind of event help could I offer?
Think of a part you've handled before: directing guests with the organiser's instructions, perhaps, or arranging materials to match a layout. Describe what you did, rather than the whole occasion. Helping at a gathering doesn't mean you ran the production, and you don't need to suggest that you did.
What would you need to do that part well? At a welcome table, you'd want to know the entrances and where to send people. Arranging a display might need an example to follow. Those details tell the organiser both what you can do and what they need to explain.
What should I ask before joining an event team?
Find out where to meet, when you'll get a briefing and how the day runs. Agree on one contact who can settle priorities if people give you different instructions. Ask when you finish, even if the event will continue, and who takes back equipment and lists and receives your final update.
These guides don't cover alcohol service, technical installations or roles requiring authorisation or training. If the help changes, check what that means before agreeing, and stay within what you know how to do. The guide to starting event work covers coordination, changes of plan and handover, with questions to ask about the part you'd take on.