Create a workout to strengthen my upper body

If you have access to weights, a workout might start with four sets of bench press and four sets of upright row at 6 to 10 reps each to strengthen your chest and back. If you don’t have access to weights you could replace those exercises with some combination of push ups, pull ups, and chin ups. Next move into three sets of shoulder press and rear delt raises for ten reps each. Finally, do three sets of bicep curls and three sets of tricep dips for ten and thirty reps respectively. The weights and repetitions for each exercise should scale with your comfort and ability doing that exercise. 

When working out, it’s very important to use good form and not overextend yourself. When lifting heavy weights it’s a good idea to get help from a spotter, and in particular you should never do bench press alone. Don’t fall into the trap of pushing too hard and risk your personal safety - you’ll get a lot stronger if you avoid injuries!