Allows you to craft a Knowlege Book with Green Dye + Book. They are special Knowledge Books which can be stacked up to 64 (Usually, they cannot be stacked).
The Knowledge Book has no use on its own other than displaying it in an Item Frame and being interesting to own because it is normally unobtainable but can be useful in other Datapacks.
Copy the .zip archive into the ".minecraft/saves/yourworldname/datapacks" folder, where yourworldname is the name of your world.
Copy the .jar archive into the folder your Mod Loader of choice provides.
When you right click with a Knowldge Book, you will lose it. Prior to 1.21 you will lose the whole stack.