Hi Bethany,
Welcome to Modlar! The first step for downloading furniture is to find a product that has the file you are after. The easiest way to do this is to use the search bar at the top, either type in the product you are after or just 'furniture'. Then hit the search icon and once your search has been loaded, find the 'Formats' filter in the left hand tab and tick the file format you are after. This will leave you with only the products that have your file format. Click on a product and you will find the 'Downloads' bar on the right.
That should get you started. Please let me know if you have any more questions!