Black hole is super massive object. It bends space-time.
Why do we call it black? Because it absorbs all light without any reflection.
Probably the center of galaxies is super massive black holes.
In our galaxy there is Sagitarius A,
It has mass of about 4 million suns.
Black holes are born by gravitational falls of very massive stars.
Our sun can't will be a black hole, because it's not very massive.
We don't know what is in black holes.