Example: Let's say we have a Model called Car. This Car has fields that describe features of a Car for a car sales mobile app, such as Paint Color, Doors, Engine Size, Seats and Price.
If we wanted to have a section of the mobile application to show Used Cars, we would create a collection in Fuchsia called Used Cars and we would add Car records to that collection. Then in our application, we can query the Used Cars collection to access to your cars to display on your app screen to your users.
Collection querying is basically the act of filtering down the records in your collection to match a certain criteria. For example, if we wanted all cars in a collection where the Color was Red and Price was less than 20K, we could express that in our API call. Check out the API docs for records for more details.