There is dark matter and dark energy.Both energy are invisible we don’t know what it exactly is and how do they work.
But what do we know?
Space isn’t really empty . We think of space as this large empty void filled with billions of stars and plants. But in reality this empty void has matter. There is something to it.
Dark energy makes 70% of the universe and dark matter makes 25%. And as of now the normal matter constitutes only 5% of it.
Scientists tried to find out what this dark matter was composed of.
It could be cold , dust , rogue planets. But they were left to choose these random subatomic particles.
But How to detect dark matter?
That's still a question that is unanswered. But there are various experiments going on to battle this problem.
Dark matter does not absorb or emit light. That's the reason why we can't see it. There might be huge clouds of dark matter that influence the rotation of galaxies!
So let's simplify this:
- Dark energy is the humongous part of the universe
- Dark matter is the reason galaxies exist.
3 things we know about Dark Matter
- It exists
- Interacts with gravity
- There is a lot of it!
Dark matter doesn’t not interact with light and matter , and we can't detect or measure dark energy. But it's effects are definitely out there. And it's strength or its effect on the universe is getting powerful day by day.
They are complex matter which interacts with themselves. They may have both hot and cold particles. The hot particles are known as "neutrinos" and move at the speed of light, but they have no mass. Cold particles are known as WIMPS - Weakly Interacting Massive Particles
The Xenon100 Experiment
There is an underground experiment currently going on to find these particles called Xenon100
Image Source
If you want to read more about dark matter, I suggest you read the Article written by 
Sources:
Nasa
Space.com
Dark Matter Crash Course
