Your muscles move you by pulling or relaxing. That is all. Muscles cannot push. Wait a minute. I can hear you saying that muscles must be able to push.
Lets think about the muscles.
When a muscle is relaxed, it is longer and thinner. When you tense the muscle, it contracts, to get shorter and thicker. If the muscle was not attached to anything, this would not do much. When you tensed your muscles, you would just get lumpier. Luckily, our muscles are attached to our bones.