How to enter grafical root
You need root privileges to access directories like /usr/bin.
If you want to run commands as root you can type:
sudo su
and then your next commands will be run with root privileges.
You can also type sudo and individual commands to run only those commands as root.
If you want to copy files with your file explorer, run your file explorer as root; if you are using Ubuntu type:
sudo nautilus
If you are using another flavour where Nautilus is not the default file manager, type it's command after the sudo (for example: sudo caja for MATE).