The best reference is PHP.net or a good book on PHP/MySQL. First thing you want to do is figure out what information you need to have in the database.
You're probably going to need a user table and an items table at the very least. A good idea would be to have a userid field in the user table thats an "Auto Incrementing Integer" (check mysql.com for reference on MySQL).
As far as login you're going to have to decide how secure you need to be and whether you want to use sessions or cookies.
From there the coding is not very hard at all, you're just pulling things out of the database and displaying them.