Edit a page - that's pretty vague (maybe purposely so that you don't give away your idea?). Maybe you should look at this article:
https://vborg.vbsupport.ru/showthread.php?t=228112 , it shows how you can start to use the vbulletin code on your own page. As far as templates: vbulletin is designed to keep html and css in the database in templates. If you're writing your own page you can use templates if you want, but you don't have to. I think probably you would want to use them unless you have a reason not to.
This probably isn't much help, but hopefully it's some kind of start.