Black holes are normal matter with such a high density that light cannot escape from it. Like a big star that explodes (supernova/hypernova), it sometimes leaves a black hole.
Dark matter is something diffrent. It's matter that doesn't interact with light/photons. So while black holes just have a huge gravity that doesn't allow the light to escape, dark matter just let's the light pass through it like there was nothing. Okay, the gravity of the dark matter can also bend light or things like that, exactly like the normal matter, but I don't think dark matter has much to do with black holes.
That's how I understand it at least.