Log in to your site so that you see [edit page] at the top of pages on your web site. If you don't have a link to "sign in" or "admin menu" go to yourDomainName.com/sign_in.asp
Go to the page on your site you want to lock. Click (page settings).
Scroll down. Look for Security Level Needed to View Page and/or Secure by Group and/or Security Level to Allow Editing of this Page.
Click the SAVE button near the top of this form. You will be taken back to the CELL VIEW OF PAGE screen. The file name of your page appears in parenthesis in the top/center. Click it to go to your page.