Black holes

a) what are the parts of a black hole? jets of gas, accretion disk, and sn event horizon
b) how is gravity related to a black hole? Because gravity is what is used to pull obects into a black hole.
c) how can we see the holes if they are black? They are invisible but you can find them by observing the stars and gas around it.
d) what's a Swarzschild radius? It is a radius for a mass given where if you could compress the mass to fit in it no force could stop it from collasping. Anything smaller than its swarzschild radius is called a black hole.
e) how do Einstein's theories relate to this? because his laws where what was used to study and eventually find the black holes.