Admin panels, blogging, comments, forum – Underlying all of these, are just database CRUD operations (Create, Update, Delete) of database records. So if you learn mySQL and creating SQL statements (with inner joins, outer joins, etc) you’ll be able to create all these things. You may need some courses on database schema design, so you can plan on how to store the different related data and their relationships.
Pagination – again, underlying this is just knowing how to create the right SQL command to query/return only a subset of records from your database, and then you just display those records.
Security – most of security issues are from unsanitized user inputs (and/or URL query parameters) making your site open to SQL query injections. Again, you need knowledge of SQL so you’ll know how to filter out and keep your user provided data clean and sanitized before passing it to your SQL query.
So in your search, look for PHP and mySQL courses… and BUY A BOOK (or read online docs), not everything can be taught in a video course.