When your account is initially setup a password is assigned. You should change your password after you login for the first time. Shutting off your terminal does NOT log you off. Another user could turn on your terminal and use your account. You can enter your commands in upper or lower case.
Commands usually have qualifiers and parameters.
Qualifiers give more information on how to execute a command. Parameters specify what the command acts upon. The DIRectory command gives a list of files or information about a file or group of files. Each block is 512 bytes or characters. The type command displays the contents of a file or group of files on your screen.