How to track user interest and display products based on their interest

I have an e-commerce website and I need to display products in homepage based on user interest like advertisement showing on facebook and google based on the search we did on the internet.

Is there any API from facebook or google or any website for fetching user interests?

I have wondered how facebook, google, and booking.com collaboratively tracking us even if they are different companies.

Is there any common gateway or common interface where these big companies share user info by making a system with cookies to track among all as a centralized big data model for behavioral advertising?

I am looking for answers from experts for this. I really need to build a system for tracking user interest based on their search on google and other websites.

So you need to use something called recommender systems, using a machine learning algorithm, you'll recommend products to people based on ratings and interest. by using previous data of the same user or other users (just like when you get recommended videos on youtube).

this topic is too big for me to explain it step by step in here, and you need to first have a good understanding of primitive machine learning such as classification, regression ... etc

so if you're interested make sure to check a coursera course called Machine Learning (Stanford University) it's taught by machine learning rockstar Andrew NG, and it doesn't only teach you machine learning, but it takes you from somebody with no idea on the subject to an expert (technically) the course used MATLAB/OCTAVE and it has an entire section on Recommender Systems which is what you need, after you've finished just implement what you learned in the language of your choice !

PS: you can always look up tutorial online for implementing Recommender Systems, but you will waste so much time because you would have no idea about what you're doing without understanding the theory which you will master in the course I've recommended, the course can also be found easily on youtube. but taking it for FREE in coursera will help you more because you'll have hands-on programming experience, on the different subjects.