"Peng" is an onomatopoeic expression which translates into English as "Boing", "Bump" or even "Peng." It describes the buoyant energy that protects a body which is relaxed and properly aligned. Peng is seen here as an action. But it is really an internal power ("jing") or quality "gong" that is developed through consistent practice. When peng is properly manifested, any external force applied to the expert's body will seem to float and fail to uproot its target.
When performing "Peng" or "Ward Off", it is important to stay relaxed and pay attention to the proper alignment of the arm with the rest of the body. Feel the connection to the ground. Do not think about pushing anything away with the arm. The power of peng comes from the legs. The direction of the peng comes from the waist and hips. The expression is in the round and relaxed arms.
Under no circumstances should you try to increase the tension in your shoulders or arm.
For beginners learning the 24 form tai chi or the 32 sword routine, there is no better reference than these books and videos by Grandmaster Shouyu Liang. Grandmaster Liang is the only person that I know of in the world today who has been teaching the 24 form tai chi constantly since it was created in 1956.
Simplified Tai Chi Chuan, by Liang Shou-Yu, is the definitive reference manual for those learning or teaching the 24 form or the 48 form. The book and the video include the 24 posture routine with martial applications, as well as the 48 form. The book also includes some history, philosophy, basic exercises and important principles of alignment and movement.
"Taijiquan: The Art of Nurturing, The Science of Power" by Master Yang Yang, is one of the most important books for any student or teacher of tai chi to have in their library. It presents the theories and principles from both Eastern and Western perspectives, examining mental, physical, and spiritual aspects. The book also gives priceless advice on everything from proper practice methods to finding a good teacher.