How do you kiss a girl for the first time?

Me and my girlfriend have been going out for about a month and we haven't kissed yet. She wants to kiss for the first time next week. I've never kissed a girl before so I have no idea what I'm supposed to do, or where we should do it. We goto a Christian school and any kind of PDA is of course punishable. There is a staircase where everyone seems to always kiss there but I don't know how we both can get there without anyone there. I'm thinking about texting her to ask to use the bathroom so we can meet up there but I dunno if thats a good idea. Any help would be appreciated