I use a software called Bricklink Studio 2.0, which I design, render and make instructions in. 

If you order a set with instructions and a parts list, you can buy the Lego pieces and build the set IRL! You will have downloaded a .txt file as part of your purchase, or I will have sent one over Discord once your design is complete. Bricks are bought on bricklink.com, so you must have an account there to buy bricks. Full instructions can be found on the dedicated FAQ page.