How does the compared products work?

I can’t seem to figure out how to properly setup the compared products, does anyone has a turtorial for this ?

Also i have a question that i can’t seem to figure out.

Is there are difference between a listing website and a comparison website?
Normally for comparison website a webshops has to submit their products in xml or cvs or in some cases by rss feed.

1. How does the webshop notifies on price changes?
2. is their a difference between listing and a comparison
3. How does price comparison works for comparing products?
(because it looks like i have to add products manually under the page “compared products” to be able to compare?

So can someone explain me how the comparison structure works?
Adding listing, Comparing Listings, Searching listings

Hope to hear soon