Think of the shell as Super-Dooper DOS. You enter a command, the shell checks it out, then the kernel does the rest.

Most Linux distributions use bash as the default shell. There are many others. Two of the most popular being pdksh and tcsh (pronounced tea-shell). This manual only covers the bash shell since the purpose of this manual is to get you using Linux as quick as possible. When you become confident with Linux, finding out about the other shells is a piece-of-cake.

The shell's job is to interpret the commands and run the programs you request. Linux is a multi-tasking OS (meaning you can run multiple programs). Linux was also designed to be a multi-user OS, meaning it can run multiple shells. Each user is allocated his/her own shell at login. As a user, you have access only to the programs you're running, not the ones others are running. The programs are kept separate because they are "enclosed" in a "shell".