Create a private area

Hi buddys,
I need some help to modify my WP. I would like to create a private area.

Exactly what I want is create a widget with a link to a private area. The first thing you will see after click on the link is a page where you have to put your username and password(I´d create the users before). If the user and password are correct, you will be redirect to a specific page, if they are wrong, a message will appear telling you that you must be our customer to see that information.

How can I do all this? What modules do you advise me?

Thanks in advance