source: https://devhints.io/pacman

  pacman -Syu <pkg>     # Install (and update package list)
  pacman -S <pkg>       # Install only
  pacman -Rsc <pkg>     # Uninstall
  pacman -Ss <keywords> # Search
  pacman -Syu           # Upgrade everything

  pacman -Qe            # List explictly-installed packages
  pacman -Ql <pkg>      # What files does this package have?
  pacman -Qii <pkg>     # List information on package
  pacman -Qo <file>     # Who owns this file?
  pacman -Qs <query>    # Search installed packages for keywords

  pacman -Qdt                  # List unneeded packages
  pacman -Rns $(pacman -Qdtq)  # Uninstall unneeded packages

Avoid orphans by using pacman -Rsc to remove packages, which will remove unneeded dependencies.

  pactree <pkg>      # What does pkg depend on?
  pactree -r <pkg>   # What depends on pkg?

Things to try:

pacman-key --refresh-keys
pacman-key --list-keys
edit /etc/pacman.d/gnupg/gpg.conf

Re-initialize keyring:

rm -r /etc/pacman.d/gnupg
pacman-key --init
pacman-key --populate archlinux
pacman -S archlinux-keyring