A chest roll is where the frisbee rolls from one hand, down your arm, across your chest and then out onto the other arm and hand. Ideally, the disc will touch your body the entire way across. However, that level on control is hard to master, even after 20 years of playing.
To practice, face the wind. Toss the disc on a steep angle so the wind will blow it back to you. Consider which direction the disc is spinning and toss it so it is close to the hand that will propel it across your chest. That is, left hand for clockwise spin and right hand for counter clockwise spin.
Next, hit (brush) the disc to give it momentum to traverse your arm, chest, arm and other hand. This initial contact is very important because, if the disc makes it at least across your chest, it is easy to save by pulling in your far hand and doing an airbrush. However, if it doesn’t make it to your chest or hits your chest and falls, it’s nearly impossible to get the disc back in flight.
As you practice, you’ll find that you can put the disc back into the air with the far hand. This can lead you to multiple chest rolls, air brushes, or trick catches.