Here are a list of useful commands to be used with pacman.
pacman may require some specific settings if your environment is behind a proxy, so you should have a look here.
Update and install the list of package.
Perform a full upgrade, is necessary if some libraries are missing to recompile systemt properly.
Install a new package.
pacman -S $PACKAGE
Remove a package.
pacman -R $PACKAGE
Remove a package and its dependent packages.
pacman -Rs $PACKAGE
Look in package database for packages based on given keyword.
pacman -Ss $KEYWORD
List of packages installed as dependencies but not used anymore.
List of packages explicitely installed, and not needed by other packages.
List of packages with given keyword.
pacman -Q | grep $KEYWORD
List of files installed with package.
pacman -Ql $PACKAGE