Few questions for default/list.html

[i732]

I have a few questions on how to structure the data, I basically want to create a list of my .md files inside dropdowns on the list page by category like this:

This is the structure I’m looking for:
products:
Type1
-> product1.md
-> product2.md
Type2
-> product3.md

So two questions:

1. How do I structure my files to do this?
2. Where should I set my images to grab these, in the static directory or somewhere else?