Hi andriyb!
The answer to your first question is YES. We can divide the aliens in different races.
They are many races of aliens in the Universe (that's true), but only a little of them visited us in the ancient past and in the modern past (~1934-today). Why a little of them? Because, they lived nearby (on Mars or maybe on Venus (that's what the abductees of modern time said)). Many alien civilizations are too far away from us and they can't reach us. Why? Because, some of them are like us, which means that they don't move farther from their planet. They maybe reach their second planet, but they are not yet ready for intergalactic yourney, and that's why they are like us. Some of them are more developed then others and that's why they can travel around the galaxy's.
This thing about aliens is a little tricky. Today, we can't know much of them. We can only analyze the videos, photos and testimonials of people who saw them and then make a conclusion. That conclusion might not be the best, but we can get closer to true. I know that, because I read many books and watch tv programs about aliens.
