The Terminal in OS X

Mac OS X is UNIX-based, and Terminal gives command-line access to the UNIX core. If you want to learn to use Terminal, look for books on UNIX or using Linux from the command line.

 

As above, its command line driven and not the easiest of things. Its also very easy to screw up your system by running commands that you can 'copy and paste' in without really knowing what your doing (I am not accusing you of this)

Also, be aware that there are different versions of the terminal. I believe Mac uses the bash verision but might be wrong

This is a good place to start

 

I found this pretty handy for learning the basics (it's written for Linux, but you can figure it out. The commands are the same

http://www.ee.surrey.ac.uk/Teaching/Unix/unixintro.html

 

Think of the terminal as the command prompt in Windows.... Except with a lot more power.
You really dont need to mess with it. Sure they are a few nice commands that help change the way OSX looks and feels, but there are safe ways to do these kind of things.

 

Well it's good you're looking into terminal, it's very important to be familiar with Unix if you are going into the field.

Terminal is a command line interface (CLI) to execute more complicated operations.
Like most operating systems Mac OS X is based on Unix, ( More specifically BSD, a newer version of Unix)
Read some introductions to Unix and BSD, Then read some Unix or more specifically BSD Terminal tutorials