Wizard of the Coasts have released the core rules for the latest edition of Dungeons and Dragons under a Creative Commons license. It’s great starting point for those looking to get into Dungeons and Dragons or RPGs more generally.
The actual SRD documents, for both 5.1 (2014 D&D) and 5.2 (2024 D&D) can be obtained from the following link: Dungeon and Dragons SRDs.