I don't get how to do this.

Question

Use these numbers to get the answer showen below. However, don't stick numbers together.

Try to get: 22
Using: 3, 6, 5, 5, 0

The teacher gave us the answer but I don't know HOW this works:
3! + (6*5) - (5+0)

Answer 1

I just need to know how ! works.