As far as I know, Dark Matter and Dark Energy arewhat we need for our theories of the universe to work, but matter has mass and energy doesn’t are the main differences. But it’s not my strongest area so I may not be spot on!
We need both dark energy and dark mass to understand how the universe is behaving. For example, we can work out how much mass galaxies should have because of how they move and their gravitational effects. Yet when we try to look at the galaxy, there doesn’t appear to be enough mass. So there must be some extra, ‘dark matter’ that is there but we can’t see what it is.
Similarly with dark energy – we know how much energy a system should have. In particular, we know how much energy there should be in the universe from how fast it is expanding. Yet when we look for this energy, we can’t actually find enough. So there must be some extra ‘dark energy’ that we can’t see.
So to put it simply, dark matter is matter that we know should be there but we can’t see, while dark energy is energy that we know should be there but we can’t see. I hope that makes sense thisura, and send us a comment below if you need a bit more explanation and we’ll do our best.