Q1. Muscles are made of muscle cells that are able to contract. They are only cells in the organisms able to do that. Due to contraction, cells change their shape and length. This enables some organ activity (such as heart, or many other organs that are surrounded by smooth muscles that helps them perform their function) or body movements.
Q2. Striated muscles are called striated because of the series of sarcomeres, basic units of striated muscles. They are made up of long cylindrical fiber and attach to the bones. Contraction of these muscles is voluntary except for the heart muscles. During these contractions, the muscle is extended by the action of an antagonist muscle.