So what exactly does it do? I know it gives better throttle response... but how?

And how would I go about installing one? Can I do it myself? Or would I have to take it to a shop?

 

Yes, you can install it yourself in about 5 minutes.
Regarding what it does, please use the SEARCH function.
This is probably one of the most frequent posts on the site.
You can buy one from TVTdesigns.com
I'm sure they are more than willing to tell you what it does.
Not too long ago I think they were offering a 15 day free trial.

 

tvtdesign.com

Improves throttle response. Makes the car feel more lively. 15 min install, even less if you have small hands.

Anthony

 

look for a used one.. its a much better deal!