Core Rules
The Core Rules detail the minimum additions to Dungeons and Dragons (D&D) in order to play Pokémon 5e. They cover things such as creating a character, catching and leveling up Pokémon, and how to conduct combat.
Pokémon has many mechanics. To simplify the system, not every mechanic is represented in the Core Rules. However, the community has adapted many mechanics into D&D, listed as optional Supplements. Pokémon 5e is designed to be played with as many or as few of these supplements as you want!