If you are in a jurisdiction where downloading ROMs of games you don’t own is legal or you are certain of your use case:
For absolute beginners who found the All NES Roms Archive.org search result, here is the simplest 5-minute plan:
Once you master one game, you can consider the full archive.
Archive.org (also known as the Internet Archive) is a digital library offering free public access to a massive repository of multimedia. Founded by Brewster Kahle in 1996, its mission is "universal access to all knowledge." While best known for the Wayback Machine (which archives web pages), it also hosts millions of books, movies, music recordings, and—crucially—software emulation packages.
Unlike torrent sites or shady ROM forums, Archive.org operates in a legal gray area explicitly designed for preservation. They host ROMs under the guise of "educational preservation," often leveraging exemptions in the Digital Millennium Copyright Act (DMCA) for obsolete software.
However, "obsolete" does not mean what you think. Nintendo aggressively protects its intellectual property, and while the NES is over 35 years old, many games are still commercially licensed via Nintendo Switch Online, NES Classic Mini, or compilation discs.
Use No-Intro DAT files (available from datomatic.no-intro.org) with a ROM manager to:
A complete licensed NES set (US + EU + JP) is ~1,350 unique games.