I am the developer of Sitelok and glad to answer any questions you may have. For general support its quickest to contact me directly via https://www.vibralogix.com/company/contact.php.
Sitelok allows you to create pages on your site that are accessible to members only, requiring them to login. You can allow users to register themselves (with or without admin approval) or charge for access using Paypal or Stripe. Many other features and plugins allow you to do a lot more than just securing pages too.
As Norm mentioned Blocs allows you to easily add snippets where needed for Sitelok and other scripts and really makes Blocs a great basis for web apps. The ‘Using Sitelok with Blocs’ manual explains the basics of securing pages and adding registration forms to your pages. I will be updating it a little over the coming weeks for the newly released Sitelok V5.5 but its still valid.
The first few sections of the main Sitelok manual provide an overview of how Sitelok works and how to use the control panel dashboard. Its mostly a reference and has become quite large to cover all the features that have been added so you don’t need to read it all so don’t get scared!