matchstick unix the online unix manual, with tutorials, help, and training in unix commands. Unix in Summary

An introductory tutorial on Unix...

Selecting a Shell

Regular Expressions...

Perl and Unix...

Help with vi...

Shell scripting...

The 10 Unix commands every beginner needs to know...

The 10 most misunderstood commands...

The 62 Core Commands

Commands by Category

Alphabetic list of commands...

Unix in Summary

User

::: The user types input and gets feedback on the screen

Shell

::: The shell is the User Interface, or UI. It is not a GUI (Graphical User Interface) because it is entirely text-based.
::: Although there are no menus or trash cans on the screen, the ideas are the same in Unix as they are for Windows or Macintosh - You can:

create or delete files

move them between directories

open and edit them using programs
::: The shell interprets the input and calls the various commands, which are all essentially mini programs

Programs and Commands

::: The programs make system calls to the kernel, such as:

Get time and date

Write to a file

Run an executable file

Display information

etc.

Kernel

::: The kernel is in charge of:

Maintaining the file system

Handling interrupts and errors

Allocation of memory and resources

Communicating with the hardware via device drivers

Hardware