Not a good post for /s/Linux4newbs without explanation. This is risky when you don't know what you're doing.

Also don't sudo su, use sudo -i or sudo -s instead

OK now if you do this wrong you can make it so you can't boot an existing OS. Now before doing anything make sure you know which OS's are actually on your computer. Now I found this method helpful when reinstalling Antergos and if you have an old grub file for ubuntu you might have an error trying to install xubuntu or other fork since they use the ubuntu grub. So if you install and arch dist and have an old one you removed if you don't delete the old grub entries it might not let you do a good install of a new OS. So take care this will delete what you tell it to and it will be gone forever. This is safe since I've already used it and didn't realize that I had 5 old grub files in my efi/boot partition. Hell before this I would just format the entire drive and install everything from scratch so this is saving me about 3 hrs of reinstalling 2 or more distro's over because I did not know these commands existed.