How can I implement a required disclaimer page?
I'm assuming that once someone "Agrees" to your terms, you do not want them to have to agree on subsequent visits?

I'd like to recommend a forced registration. You can restrict the contents of your website to authenticated users only. To do this - go to admin/people/permissions and uncheck all permissions for anonymous users.

If you do not want to mess with site permissions, you can check out a great module:
https://www.drupal.org/project/anonymous_login
Anonymous Login will redirect anonymous users to the login page whenever they reach any admin-specified page paths.

Then I would customize your user registration process accordingly. Make it as lightweight as you want. I would check out the Site Disclaimer module to add your site terms functionality:
https://www.drupal.org/project/site_disclaimer

Also - if you're looking for a quick way to make the login/registration pages nicer - check out the "Better Login" module.

Depending on your version of Drupal - check out the "Agreement" module.
The Agreement module allows the administrator to present a text-based agreement (think "Terms of Service") that users of a particular role must accept before they are allowed to access the site.

Let me know if you would like more clarification. I hope this helps put you in the right direction, but you didn't provide much background info for me to help. (i.e what have you done so far, etc).

-Wrench