Carbon fibers woven together (https://dragonplate.com/sections/technology.asp)
Stronger by weaving multiple fibers into one pillar (http://info.craftechind.com/blog/the-rise-of-carbon-fiber-reinforced-plastics)
Like I stated earlier carbon fiber can be fabricated in many different forms for different purposes like yarns, weaves, braids that are in turn used to create other composite parts usually with the use of epoxy due to it's good compressive and shear properties into a matrix. There are many methods to do this like vacuum bagging, wet layup, resin transfer, insert molding and many more.
carbon fiber epoxy matrix (https://dragonplate.com/sections/technology.asp)
carbon fiber sheet with epoxy resin and hardner (http://www.cjcompositestechnology.com/carbon-fiber-epoxy-resin-kits/plain-weave-carbon-fiber-epoxy-resin-kit-with-6-oz-resin)
The modulus of elasticity of carbon fiber is about 225 GPa with an ultimate tensile strength of 3.5 GPa and can be even higher by using specialized heat treatment processes. in comparison A36 steel only has modulus of elasticity of about 200 GPa and a tensile strength of 0.4 Gpa. It's so strong due to the fibers being composed of carbon atoms bonded in microscopic crystals aligned parallel to the axis of the fiber which leads to the large strength to weight ratio.
Tensile strength vs Tensile modulus of different types of Carbon fibers (http://dare-bikes.com/dare-carbon-tech/)
In cars specifically, the woven carbon fibers are combined with plastics, such as epoxy due to it's low density and compressive and shear properties as explained earlier. This way various pieces can be shaped into whatever the carbon fiber is being used for. Sometimes a plastic mold will be wrapped with carbon fiber sheets to save money and other times pieces are molded with 100% carbon fiber to make the most out of it's properties. Today it's being used in various different part's all over the car even wheels and the body. it's properties help create a light but rigid car, sometimes having a higher energy absorption than steel which is why it's mostly used for higher end cars but is being adapted in regular cars today.
mold being covered with carbon fiber and epoxy (https://www.youtube.com/watch?v=9F1Hp_nqqOY)
Pagani Zonda with an all carbon fiber body