I've a site and I would create a simply "Members only" page. I would add a protection to a page content so only editors and administrators can access.
This page should be visible to all users, but when a guest click on it, the page content is protected by username/password. When user fill these fields, the page automatically redirect to protect content.
Is there a plugin, or method, that I can consider?
Wordpress has builtin "password-protect page" feature. If you are using some kind of a standard theme, all you need is to set a password inside a "publish" box at the page editor page (password field is hidden behind some link).
There probely is some plugin for this kind of stuff, i mostly build my own themes, and implement it there.
if its just one page you want to protect, you could make a own template file for that page. if the page name is "secrets", you could in the teames folder copy the page.php (or index.php) to page-secrets.php, and add some php code to protect that page.
a relly simple version could be:
where ... is the copied content from page.php (or index.php) between the get_header(); and get_footer(); rows
I advice you to use the "members" plugin
http://wordpress.org/extend/plugins/members/
it allows to protect page with role. If you protect page with 'subscriber', user must be logged.