XML : Retargeting banner tutorial

First; I wish everyone a happy new year!

And now for my very simple question; Does anyone know a good tutorial or how-to on creating retargeting banners?

I've looked allover Google but I can't seem to find any good tutorials on this topic. What I'm (or wanting to) building is this:

On website A a visitor sees an Hotel. The visitor moves on to another website (B) and sees an ad for the Hotel he just viewed on website A. The banner thus shows retargeting content. The XML is very straight forward and every hotel has an ID.

Does any of you know a good tutorial that would get me in te right direction? My experience with coding is like this:
HTML(5) Excellent
CSS - Excellent
XML - Very good
PHP - Good
JS - Good

Thanks in advance!