Chin-ups a great exercise to get stronger, and gain muscle.

Chin-ups is performed by you go up to  the pull-up bar with the palms facing your torso and a grip smaller than the shoulder width.

As you have both arms extended in front of you holding the bar at the chosen grip width, keep your torso as straight as possible while creating a curvature on your lower back and sticking your chest out. This is your starting position. 

When you breathe out pull your torso up until your head is around the level of the pull-up bar. 

Use the biceps muscles in order to perform the movement.