To lock all pages containing a certain word in the title, fill out the form like so:
Or, to lock all pages that use a certain custom template, use this:
3. Submit the form to create your lock, then proceed by configuring keys as appropriate.
If you'd like to use something other than the title or template to activate this lock, take a look at Shopify's Liquid documentation for pages - you can adapt your custom lock for any of the page attributes listed there.