sudoer

I need assistance. When I try to use my user password in the terminal, I am told I am not on the sudoer list.
Here is the command I enter:
"sudo grub-install /dev/sda5"
It asks for my sudo password and I enter my user password, and i subsequently informs me that I am not on the sudoer list. I haven tried entering my root password to no avail.
I also have MManjaro Linux installed and in its terminal I entered this:
"sudo pacman -S grub"
"sudo grub-install /dev/sda"
"sudo update-grub"
Subsequently, if I were to enter:
"sudo grub-install /dev/sda5" followed with:
"sudo update-grub"
I should then be able to boot into either Mageia or Manjaro Linux. Loooking around I found how to edit by hand the 'sudoer.d' folder, but I also discovered I do not have the authorization to do anything. I am back to quadrangle one. How do I get permission to edit the aforementioned file, so I mayenter those commands which will allow me to dual boot.
Here is the command I enter:
"sudo grub-install /dev/sda5"
It asks for my sudo password and I enter my user password, and i subsequently informs me that I am not on the sudoer list. I haven tried entering my root password to no avail.
I also have MManjaro Linux installed and in its terminal I entered this:
"sudo pacman -S grub"
"sudo grub-install /dev/sda"
"sudo update-grub"
Subsequently, if I were to enter:
"sudo grub-install /dev/sda5" followed with:
"sudo update-grub"
I should then be able to boot into either Mageia or Manjaro Linux. Loooking around I found how to edit by hand the 'sudoer.d' folder, but I also discovered I do not have the authorization to do anything. I am back to quadrangle one. How do I get permission to edit the aforementioned file, so I mayenter those commands which will allow me to dual boot.