This data pack causes Experience Levels to regenerate, at a rate of 1 per second, up to the highest Experience Level you've achieved, or the configurable maximum, whichever is less. This means that initially you'll have to gain experience from the usual sources, such as mining and smelting, but once you reach the maximum (Level 30 by default) you won't have to worry about EXP again.
By default, the maximum Experience Level this data pack will regenerate to is 30. If you'd like to change that, you can find the configuration file at "data\qi\functions\config.mcfunction" within the zip file of the data pack.
More information about data packs and how to use them can be found on the official Minecraft Wiki.