It does require a username and password.

Hence I couldn't reply to this posting until I'd logged in. Before I logged in I was just "The Public", but after logging in I was a "Registered User", and the permission on the forums only allows posting by registered users.

So for your site you can change the permissions to just allow registered users to see a section if you wish to.

Or, take it further by only allowing specific users access, by managing the membership of your site (i.e., controlling exactly which users are members of your site, then setting the permissions to only allow Members to read sections of your site).

On your site you can control the Membership Policy - i.e., whether users can become members at all, whether they need approval from you, or whether anyone can be a member without approval. You can also invite people to be members, as John covered above.

Thanks

Joe