Q: How can I add add repositories from arch into manjaro?
I would like to install a few applications from arch repository without having to compile. Because I am a Windows user who new to arch base distros, I would like to get my feets wet before trying to compile my own package.
You don’t need to add repositories from Arch to Manjaro like PPAs on Ubuntu, you just need to activate the AUR (Arch User Repository) and that’s it: all AUR packages become available to you.
Whether or not you have to build or install is up to the package maintainer, and for you the only difference is that packages that are “built” just take a little while (up to quite a while) longer to install.
When you choose to build packages from AUR you need to know that every time you update your Manjaro system - there is a chance that your AUR packages will need rebuild and therefore - when an AUR package acts weird after an update - rebuilding said package is often the solution.
You cannot - and most importantly you should not as it will cause irreparable damage to your system files.
Manjaro repos is drawn from Arch and synced several times a day from Arch stable.
Except from some obvious packages like kernels, kernel modules, nvidia drivers, a few Arch specific packages (e.g. arch-install-scripts) and Manjaro specific applications - there is nothing in the Arch repo which is not available in Manjaro repo.