How to load items on page only when page is scrolled down?

[WaRmUp]

I'm new to ASP Web Pages. Trying to build a shopping like website. I have created Databases first, Now what I want is to display "some" items of users' interest only so as to keep page light. Later when user scrolls down, next "x" number of items are fetched from Database and are shown to the user. Its like something you can see on myntra.com, but definitely not like on ebay.com where number of items are fixed on one page. I know it will use javascript but can't figure out the correct timings of firing events and adding more items to page?? I saw on stackoverflow itself about scroll down event, but I think that was related to a particular ID on a page.