Where to begin


I was hoping for some advice on how to approach a new web site that i would like to develop. i really don’t know where to begin. i have some experience in basic web sites but this one will need a login for some of the features. i would like some pages to be accessible to all, and a few others to be available by a login. this login would be granted after a membership fee is paid. the type of info provided via login will be viewable lists and also .pdfs.
As always any guidance would be helpful.
thank you