This is one of the most effective exercises for chest muscles. However, given its difficulty level, it's not for beginners. If you're a beginner, we suggest doing other chest exercises for a while before you attempt this exercise.
Dips always need to be done in a controlled manner. Otherwise you risk injuring your shoulders and even hyperextending your pecs. Thus, nice-and-steady is the key to executing this movement.
Another important item worth mentioning is related to the position of your elbows. Namely, if you keep them tighter (closer) to your sides you will be hitting your triceps more. If you spread them outward, you will be hitting your chest mostly. Thus, keep this in mind when executing this movement.