Western digital my passport essential SE hard drive

so i've finally decided on buying this external hard drive. And i know ive recently posted a similar thread on the apple time capsule, but i quickly want to double check afew things before i buy this one tomorrow. I've watched videos showing how this WD drive backs up everything from your computer automatically, however the reason i want to buy this, is not just to back my data up but because my internal hard drive is full i need to know if i can add extra music/photos straight onto my macbook as if the WD drive was actually adding storage to my internal hard drive. I presume you can, but will it be as simple as instead of choosing my mac HD just chose the WD HD. Also say if i put a cd in my mac to add to my itunes library will it just automatically import it as it normally would if the WD drive is connected.
And finally how do i format this to mac which it says you have to do.
sorry for the length, and thanks in advance for any help.

anyone ?

You can of course move and load your iTunes library and iPhoto library to an external hard drive. Same with some other applications. However, you're only placing a "band aid" on the problem. You really need a larger and faster internal hard drive not an external one. Also an external hard drive is going to be many times slower than an internal drive.