external harddrive networking help

Please bear with me, I am not so tech savy when it comes to networking. All I want to do is setup an external harddrive to my router and access its files through the network with a MBP. What type of ext hd is recommended for easiest install? Or a simple step by step instruction how to setup? I would assume time machine would not require any type of setup, but I am not looking to spend $299. Thanks so much in advance!

-clueless blonde