[newbie] How to use membership data with my own application?

Hi, I am developing a web app with form authentication and membership, but after reading several articles about membership I still couldn't figure out what it can do besides login/register. My current workaround is create my own User table with information I
want to collect from the user, and link it with the membership database
by the username after the user loged in. I am using the membership api
just for logging in and register but I think this is not the right way
to use it.
Questions:
1) Where is the membership data stored? I created several users for my app and they works fine, but the following queries on the membership database returns nothing:

select * from dbo.aspnet_Membership
select * from dbo.aspnet_Users

2) How to add more information about the users? For example, I want to allow the users to add their web site address, blog address, etc. Can I extend the existing table (and which table)? How t ...