[Asphyx]

a rom is flashed into the phone...it contains a a bunch of sys files and any oem (third party applications) that got cooked into the sys...

A Kitchen is bunch of sys files uncooked and you can add or remove 3rd party apps that are included in the kitchen to customize the rom...

Basically a kitchen makes the rom your going to flash...

If it's just a rom you can't really change what is in it. just flash...
A Kitchen lets you pick what is included in it.

I suggest you start off using ROMs first and when you get more experienced and know what 3rd party programs you want to remove or include then move onto trying a kitchen.

I personally like to flash bare bones ROMs and install what I want myself.
Makes it easier to upgrade to latest versions as they come out...
If it is cooked into the rom sometimes you can not upgrade the program.