The stimulus for muscle growth is resistance training. This could be in the form of calisthenics, weight lifting, or any other intense physical activity.
After the stimulus has been introduced, your muscles now have to recover. This usually means resting, hydrating, and replenishing nutrients in your body.
Lastly, muscle adaptation means that your muscles will change in a way that'll make them better prepared to handle the stimulus again, should it happen again in the near future.