Yay is an AUR helper that you can use as a replacement for yaourt (deprecated). It's not available in the Arch Linux repositories. So If you recently installed Arch, you can follow the instructions in the GitHub repository.
First of all, you need to clone the PKGBUILD and run
makepkg script for building the package.
Git is a dependency of yay and installations from AUR are made through a fakeroot environment, so you need to install both packages. On a new Arch installation, Git and fakeroot are not installed by default, and you also need git to clone the PKGBUILD from AUR.
makepkg, its dependencies need to be installed. You can install the base-devel package group which includes
fakeroot or install them individually.
$ sudo pacman -S git
$ sudo pacman -S base-devel
binutils, make, gcc, fakeroot:
$ sudo pacman -S binutils make gcc fakeroot
$ git clone https://aur.archlinux.org/yay.git
$ cd yay
$ makepkg -si
Yay is installed and you can get packages directly from AUR using this helper.