yaourt is a package manager in ArchLinux complementary to pacman.
It is useful to get packages that cannot be found through pacman.
yaourt may require some specific settings if your environment is behind a proxy, so you should have a look here.
Installing yaourt is tricky. You need first to install package-query which is a dependency.
So to install package-query first be sure to download PKGBUILD and tarball from here.
tar zxvf package-query.tar.gz
You will find a pkg file, you can install it directly with pacman as root.
pacman -U package-query.pkg.XXX.tar.gz
Then you can install yaourt by downloading first PKGBUILD and tarball here.
tar zxvf yaourt.tar.gz
You will find once again a pkg file, install it with pacman as root.
pacman -U yaourt.pkg.XXX.tar.gz
And you are done.
yaourt is honestly great, it will soon become your best friend on Arch. It automatizes a lot the installation process of a bunch of packages and functionnalities by fetching packages with curl from remotes, compiling everything, making pkg files and install everything with pacman.
Here are some commands to use it.
Search a list of packages with a keyword.
yaourt -S $KEYWORD
Once this is used, you will have to choose among a list of packages what you want.
Update system using AUR packages.