Before I tell you how to create and manage users, let's talk about the purpose of user
accounts.
Why do we have them?
Well, on a Linux system, you need security principles, and user accounts are just that.
They are used to provide people or processes access to system resources.
Without security principles, it would be like 1981 MS-DOS.
Everybody has access to everything.
It doesn't work that way on a modern operating system.
On Linux, processes are using system accounts, and people are using regular user accounts.
So there are user accounts everywhere.
These process system accounts normally are installed automatically when you install software,
and the accounts for people, well, you need to know how to create them manually.