Well all of it actually...
But close hands=more inner chest.
Shoulder width=more tricep
Wider = more chest/outer chest
Decline= upper chest

Hope this helps bro..

I think it trains chest and tricep muscles. It is just the focus that differs. Because you push, bicep is not working out that much. (Different if you do 'pull' workout).

There are different pushups for tricep and different part of chest.

All of the above:)

You can do 'dumbell like' weightlifting using the other hand. Sit on a chair or bench, place your right arm on your thigh, and grab thw palm of your left hand. Lift it as you lift  dumbell, and increase your left hand power to add more weight for the right hand. This way, you also train your left tricep, while working your right bicep.
Sorry for my english, but it is actually easier done than said.😺

You can use pulling row or towel to train bicep. Position your right arm just like mentioned earlier, grab one tip of the towel, and hold the other end of the towel by your left hand. Pull it by your right hand, and hold by left hand.
Hold stronger to increase the weight.

You can do chinups with your palms facing towards you