Yaourt

Yaourt is wrapper for pacman that allows easy installation of packages from the AUR. AUR packages are, simply put, just install scripts which fetch the source code, compile it and generate package suitable for installation with pacman. Yaourt automates this process, but must be installed manually through it.

Installing yaourt

Make sure you have the base-devel group installed. It contains the software needed to build other software. You also need the yajl package.

$ sudo pacman -S --needed base-devel yajl

Afterwards, get the PKGBUILD (the install script) for yaourt's dependency, package-query and run makepkg which more or less executes the script.

# Let's not bloat the current directory.
$ mkdir build
$ cd build

# This will download the PKGBUILD file.
$ curl -O https://aur.archlinux.org/packages/pa/package-query/PKGBUILD

# Always check the PKGBUILD prior to building it
$ nano PKGBUILD

# This will build the package according to the PKGBUILD. The -i option makes it get installed with Pacman.
$ makepkg -i

# Clean up
$ cd ..
$ rm -rf ./build

Now do the same for yaourt.

# ...

$ curl -O https://aur.archlinux.org/packages/ya/yaourt/PKGBUILD
$ nano PKGBUILD
$ makepkg -i

# ...

An Easier Way

Install Manjaro: it has yaourt pre-installed.