Generally tight shoes, especially pointed high heels can lead to bunions.  Foot deformities can also contribute.

What is the material that is growing inside?

The bump is from the bone itself that sticks out as it shifts position at an angle.  If you took a couple of board and had them end to end this would be similar to the position of the bones in the foot.  If you angle the upper board to the right let's say 30-40 degrees you will see the end of the board sticks out in a point.  This is what happens with the bone forming the bump.  Additional bulging can result from fluid build up (swelling) and occasionally from excess bone growth.

2. Is there a way to take care/get rid of itor at least prevent it from growing bigger?

There are a few things that can be done.  First of all make sure to wear properly fitting shoes that are wide enough in the toe area that they will not scrunch your toes together.

Stretch your big toe back towards its normal position as often as you can or get a splint to hold the toe in place.

Silica supplementation will help strengthen the connective tissue to help hold the bones in place.

3. Do you think that I might have damaged a nerve of my right big toe? Is there any way to repair it?

The nerve is not likely damaged but could be compressed.  If you can take the pressure off the nerve the numbness should go away in a short time.  If there is damage the nerves are pretty good at repairing themselves.  Some herbs that work great for the nerves though include juniper berry, gotu kola and sage leaf.