Making your muscles grow and build takes quite a lot of time, hard work and physical pain as the work you need to put in for this to happen can be strenuous.
For the muscle to build and grow bigger working the muscle to breaking point is the key.
When working out you need to get to and past the point you feel like you cant do any more.
Doing this damages the muscle cell fibres causing tears in the fibres themselves, this starts the stage of the muscle to begin being repaired by the body with the protein it has.
When the body repairs these muscle fibres when it creates and extra layer of muscle fibre cells to effectively make it stronger.
This happens with not just muscle, this happens with all cells in the body. This can be seen for example with the cells of the skin which you can see clearly from lacerations or tears in the skin known as scars.
Scared skin is tougher and harder to break and if the scar is caused by a bad cut or tear then you will noticed the scar is raised or grown outwards.
This is similar to what happens to the muscle fibres.
Over time with this happening again and again, layer after layer of extra muscle is formed which slowly increase the size of the muscle itself.
Muscle growth and repair