Composites are many different things. "Composite" just means that the final product has been made up (composed) from two or more different things.
When talking about aircrafts, then it is mostly glass fiber, carbon fiber or aramide fiber. Aramide fiber is often called Kevlar, which is a Du Pont trade name for the product. Boron fiber is also used to a minor extent, especially for helicopter rotor blades.
When talking about composites on airliners these days, then it is mostly carbon fibers, even if glass fibers have been used for radomes and many other substructures on airliners for well over fifty years.
Carbon fibers have the properties mentioned in earlier posts: Lightweight, strong, expensive, easy to mould in strange shapes, and very good fatigue properties. It is also very demanding to produce large structures since it has to be cured at a high and very exact temperature, all of it at the same time.
Carbon fiber is a very bad product for car body production. First of all it is prohibitively expensive. But even more important, it is very stiff, and when it breaks it becomes a thousand knifes, not exactly what you need in a traffic accident. Steel is almost unbeatable for a good and safe car.
In a F1 race car the driver is protected from the carbon fiber by sitting in a "bathtub" made of aramide fiber, which is also used to produce bulletproof vests and such. It has entirely different properties. A bulletproof vest made of carbon fiber would be totally useless since it would explode into small scrapnels when hit. Even if it is much stronger than aramide fiber.
For consumer products we see carbon fibers used for the most expensive fishing rods, and also some other special sports equipment where price is not important. Rackets, certain bicycle components stc. These days it is also finding its way to the most expensive amateur astronomy telescopes where ultimate stiffness and portability is more important than a few thousand dollars wallet drain.
Always keep your number of landings equal to your number of take-offs