I was given a Mac Book Pro (Retina) with BootCamp and then realized it was the only partition, so I don't have a MacOs in my Mac machine!!! Considering that, what's the easiest way to install a MacOs?
This link has a good starting point. First up, you obviously need to create a mac partition on the computer. Next, you will need to find a copy of macOs (obtainable via Mac App Store by all mac users, hence you only need to find a mac owner willing to give you a copy) and convert it into a bootable USB drive. Next, you have to boot into the mac partition on your computer and install macOS via the bootable drive.