There was nothing, then everything came from nothing, which is impossible, but it happened

This logical fallacy doesn't solve the problem, it merely pushes it back. So you say the universe can't just have been, a creator must have made it. But then, what made the creator? Are you saying the he just must have been? Well if we go along that conclusion, we can just apply it to the universe, and then there is no need for a creator.

then there were monkeys and they became humans.

No. Monkeys and humans have a common ancestor. What this means is that at one point in time there existed a certain species. Then something happened which caused part of this species to develop differently than the other. They could have been separated by a changing geography, perhaps one moved away from the other, etc. This caused them to evolve different traits best suited to survival in their respective environments (i.e. natural selection happened). Millions of years later, we're one branch, of once branch, of one branch, ..., of that species and monkeys are another.

I think that's suitable for ELI5.