Purchase Order Forms

I'm a bit of an amateur and have nearly always worked on a cash in hand basis. I have just recieved my first proper job from a nightclub in Surrey and was wondering what exactly to do once recieving this PO, I do it at work all the time, but it's slightly different seeing as the work is directly to me and I don't have a registered business. Is it as simple as just sending back an invoice with a few terms and conditions? Will I need to add VAT?

Cheers for any help!