These strips of tape are called Kinisthetic tape (or Kinesio tape) and can be stretched to a limit (i.e. 10%, 25%, 50% or full) whereby the muscle and/or tendon it attaches to stretches with it (allowing it a fuller range of movement).
They are usually used in areas where an athlete is carrying an injury, and the strip of tape 'lifts' the skin and fat off of the muscle so it can function more freely.
They can go from the origin to the insertion of the muscle for certain things, depending on what help is needed, or they can go the other way.
They won't necessarily help a muscle to become super strong if used, but they will usually restore an injured muscle to relatively strong state.