How can I make members login to view other pages?

I am setting up the forum as part of a website.  Some of those pages have sensitive material which only members are allowed to see.  I want them to login to see those pages but I don't want them to have to login twice - once to view the non-forum pages and once to view the forum pages.

Can someone please tell me what code I need to put at the top of my non-forum pages to use the same login as the forum?

What code would I need to return the user to the non-forum page once they have submitted the correct user ID and Password?

BTW, this is one heck of a good forum!