Level Up: Advanced 5th Edition is an "advanced", standalone version of the 5E ruleset. It adds more customization and depth to the game. A5E is 100% compatible with 5E, however, it is a core ruleset. It includes everything you need to play.
Open Gaming Content and Creative Commons content can be found in the separate A5E System Reference Document, available to download as a PDF. This online toolset is not the A5ESRD and should not be used as a reference for open content.