Push exercises focus mainly on pectoral muscles, shoulders muscles and triceps muscle, But let me tell you something about it, push exercises if it done only using body wright can work also on many other muscles as well, it can play a major role in strengthening your abs muscles and the rest of your body muscles.
indeed, once you progress to the more intensive types of push ups like One arm push up or semi-Planche , you no longer need to work your core muscles separately, and this is a great advantage of this type of exercise over other types.
How to start push up exercise for beginners
You have to put your self in the position of Classic push up, your arms should be straight, your hands directly under your shoulders.
now you have to push yourself forward some inches like 4-5 inches while keeping your arms straight after that return slowly to the starting position.
basically put your hands on the floor, a few feet in front of your toes, after that start crawling on your hands and your feet, this type of exercises is very good for beginners. because it uses many body group muscles at once. this exercises can be also be used by more advanced people at the beginning of their exercise and after they finish their exercises program.