Linux has over 1,000 commands on a basic service. When you migrate to the desktop, that number grows. For example, in /usr/bin on Pop!_OS there are 1,615 commands, and in /usr/sbin, there are 609.
Sudo lets you run any terminal command as another user — hence "substitute user" — but the default and most common use for it ...
Linux is a multi-user environment, which means more than one user can use the system at one time. Granted, that mostly takes the form of console access (via SSH), because you can't easily have two ...