The free way to setup WordPress user login:

You can use CaPa Protect WordPress plugin to restrict pages and categories to only WordPress users who are logged in. I also recommend using Peter's Login Redirect, which allows you to redirect users to a certain page once they login instead of the default user profile page. If your WordPress website theme doesn't come with a login field, you can install a login fields in the sodebar of your site using Sidebar Login plugin.

The $20 easy button way to setup WordPress user login:

http://premium.wpmudev.org/project/membership/

If you need me to set this up for you, feel free to contact me.