It's usually fixed by the person in charge of the system, either called the system administrator or the network manager
A password is a sequence of characters (text, numbers and other
characters on the keyboard such as # or %) that the user needs to type into
the computer after their username in order to gain access to the network
Users are usually able to change their password
regularly: this helps to keep it a secret
It is vital that the password is kept secret.
Someone who knows another person's username and password
can use them to log onto the computer, change the password and
then prevent the user from gaining access to their own files.