Every gym has a chin-up bar, which is a horizontal bar positioned above shoulder height. If you aren’t a member of a gym, you can buy a chin-up bar and install it in your house. Place it in a tall doorway and make sure it’s positioned above your shoulders.
Put your hands on the bar with your palms facing your body. Whereas a pull-up would begin with your palms facing away, a chin-up begins with your palms facing your body. This is called an underhand grip. Grip the bar comfortably but firmly, with your hands spaced shoulder-width apart
Raise your body until your chin is above the bar. Use your upper arm strength to lift your body toward the bar, stopping when your chin is above the bar. Your elbows will be fully bent. Bend your knees or cross your feet to distribute your weight more evenly.
Lower yourself back down. Using a slow, controlled motion, lower yourself until your arms are straight. This is the complete range of motion for a chin-up.
Increase your number of reps. When you can do a full chin-up, pull yourself up five times in a row, or as many times as possible. You can also do a combination of full chin-ups and half chin-ups. As your muscles gain strength, increase your reps.
You should be able to increase your reps every other week or so.
Don’t overdo it. You don’t want to tear a muscle or overexert yourself. Rest between sessions to give your muscles time to repair and get stronger.