Pacman is the actual system package manager.

Yay is an AUR helper, a program that automates all the steps of installing something from the AUR.

The AUR or Arch User Repository is a way for individuals in the community to easily distribute software, or create software installers, without going though the work of getting something into the official repos.

Here’s the first thing I do on a new system, yay -S pamac. This will install pamac, a GUI for browsing, installing and uninstalling packages. (Both normal repos and AUR)

Generally, packages from the AUR get compiled by your system and then installed. This can be really slow, hence there is often a “-bin” version of packages that installs a pre-compiled binary.

You can also find “-git” versions of packages, these install the very latest version directly from the development repo.