I need to understand the diffrent between camshaft sensor and crank shaft sensor with diagram

Even low end 4 cylinders have twin cams. So you have; the crankshaft pulley, 2 camshafts withsprockets, and a interface with the coil pack.
So, it is redundant as there are so many things that can go wrong. The timing belt tensioner comes loose and it eventually skips a tooth, which would ne too late if you didn't have them. This keeps the 2 camshafts in sync with each toher as if they are degreed off from each other, igniton parameters must be changed. Then all of this timed to the cranksaft and the ignition system.
It gets very complicated but the reason for the redundancy is for safety or if you have a twin cam.