Well, you turn up whenever you like, after 10am usually. Bring whatever bass equipment you like, pay your £10, find a place to set your gear up and then show other people your gear and check out other attendees gear. You can spend all day chatting about bass with other people as enthusiastic about bass as you are! I remember going to my first with one small amp and one bass and I was foolish enough to set up next to @cetera who has a gazillion beautiful basses and yet he, and everyone else, made me very welcome to the point that I now try to attend all the Bashes wherever they are. Believe me, it's the best tenner you'll ever spend!