We started reading the wiki page about creating packages first.
Read the guidelines we should follow.
Then we analyze pkgbuilds of others. And finally we copy/paste this code to make our own package.
Normally these pkgbuilds follow the rules but you need to check that. That is one of the dangers of copy/paste.
We will create a new package we can now all install with
sudo pacman -S arcolinux-wallpapers-submicron-2560x1440-wqhd-git-meta
General Package Building Information
On the AUR you will find thousands of PKGBUILDS.
You can use their PKGBUILDS or make one yourself.
AUR = Arch User Repository - A user is someone like you and me.
Here are some interesting links if you want to make your own 'recipe' or PKGBUILD.