good afternoon

I have the problem that my website is used by competators in the same branche to copy my articles and want to protect the pages by a username and password. 

When i want to lock the pages i get the passage: U kunt meer groepen/gebruikers aanmaken in de sectie: Toegangsbeheer, however i cannot find this option anywhere,

Can you tell me where to find this option please.

Best regards Frans