For the purposes of this example, we assume the local repository custom is located in /home/custompkgs.
Append a section for the local repository to /etc/pacman.conf
[custom]
SigLevel = Optional TrustAll
Server = file:///home/custompkgs
Create the repository root and database:
$ sudo install -d /home/custompkgs -o $USER
$ repo-add /home/custompkgs/custom.db.tar.gz
If built packages are available, add them to the database:
$ cd /home/custompkgs
$ repo-add -n custom.db.tar.gz *.pkg.tar*
Synchronize pacman:
$ sudo pacman -Syu