Can you really learn to fight by jacket of jacket on know it sounds dumb but i would like to know ?

Hmmmm......if you meant the Jacket on/jacket off training method Jacky Chan's character taught in the new Karate Kid movie, then that would depend on your instructor's knowledge and experience. Most instructors develop their own teaching methods over years of teaching and find some creative methods of training to be effective over others when teaching students with little time for training due to work. The point of the jacket on jacket off method was to use everyday movements which are already hardwired to your muscle memory, modify it and use it to defend yourself, this makes it easier for you to remember the technique and reduces the training time compared to learning a completely new movement you've never done before. This also allowed students to be able to work and train at the same time in the old days, since most martial artist also had day jobs working as laborers, ferrymen, artisans, etc. Their training were incorporated into their jobs to kill two birds with one stone. An example of this is the Eku or Oar training method used in traditional Okinawan Kobudo. Most Okinawans were fishermen by trade so using an oar was an everyday activity for them, by using this activity and modifying it to train and condition their bodies, this enabled them to both train and earn a living at the same time.