Search packages: pacman -Ss pkg1 pkg2 ...;
Install packages with updated repo: pacman -Syu pkg1 pkg2 ...;
Remove a package and its dependencies which is not required by other installed packages: pacman -Rs pkg1;
Remove a package and leaving all its dependencies installed: pacman -R pkg1;
Remove all orphaned packages: pacman -Rns $(pacman -Qtdq);
Ref: pacman on Arch Linux.