external hard drive

Can anyone tell me how I can hook up an external hard drive to keep all my content and project work?

Also - any recommendations on what type of hard drive I should consider?

Here is what I am running:

Model Name: iMac
Model Identifier: iMac10,1
Processor Name: Intel Core 2 Duo
Processor Speed: 3.06 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 4 GB
Bus Speed: 1.07 GHz