I have typed
sudo su in the Terminal, and then I typed
whoami, and the Terminal said that I am the root user. So does that mean that
sudo su makes me the root user or am I missing something?
Yes. You have the answer in
SYNOPSIS su [options...] [-] [user [args...]] DESCRIPTION su allows to run commands with substitute user and group ID. When called without arguments su defaults to running an interactive shell as root.
Note that the recommended method to do so is
sudo su -, as it starts the root shell with a login shell environment:
-, -l, --login Starts the shell as login shell with an environment similar to a real login: o clears all environment variables except for TERM o initializes the environment variables HOME, SHELL, USER, LOGNAME, PATH o changes to the target user's home directory o sets argv of the shell to '-' in order to make the shell a login shell
or directly run
sudo -i as explained in this answer.