Summarize:

Use the board to make tiny notes and very rough, imperfect drawings of the parts of the car you're most interested in. This is your opportunity to brainstorm and let your creative juices flow with the least amount of constraint. For example, if you're most excited about a new way of designing a car's windshield, focus on that aspect of your car's design. You can worry about the other parts later. If possible, have other people join you during this brainstorming so you can talk out your ideas and get input from extra sets of eyes. The easiest way to do this is usually by drawing the rough shape and outline of the car from its driver side. Don't worry about making the car perfect; just do your best to create a rough but complete drawing of the actual body of the car. This is also the best opportunity for you to start figuring out how the different components of the car you're designing can realistically fit together. For instance, if you focused on the windshields earlier, now you can figure out how to actually fit the windshields onto the chassis. Once the rough sketch of the body of the car is complete, now's the time to focus on the more minute aspects of your car's design. Draw things like the design of the side mirror, the curvature of the side of the car, or any other details you overlooked in your rough sketch. You may find that some smaller details (e.g., the curvature of the car's side) don't fit with the rough sketch that you drew. That's ok! If this happens, go back and create a new rough sketch to work with. This process helps you to figure out what works and what doesn't with your design. Draw rough sketches for the top view of the car, the front view, the rear view, and some diagonal views as well. Then, add the smaller details to these sketches just like you did with your original sketch.
Do some basic planning of your concept on a whiteboard. Start by drawing a rough sketch of the car from 1 perspective. Fine-tune the smaller details of the car per your design ideas. Repeat this process for several different perspectives on the car.