You may have decided to join the gym to get a lean body. Your trainer will tell you the workouts you should do but if you do not have a personal trainer, do not worry.
You could do the following on your own:
1. Exercise for chest: Lie on an incline exercise bench. An incline exercise bench will have a barbell on it. Lift the barbell up and slowly bring it down to about three inches close to your chest and then press it back to the original position.
2. Exercise for back: Place yourself on a seated cable row machine and pull the rowing handle into your stomach area with both your hands. Maintain a straight posture with your back perpendicular to the floor.