The theory of evolution doesn't explain the origins of life.
Before Darwin, as right now, no one knows for sure how life got started.
The theory of evolution states that species adapt to the enviroment, and changes appear due to natural selection, which is to say that the best adapted specimen lives to have more offspings that perpetuate his features.
Also at the time of Darwin, genetics didn't existed, so he struggled to find a way to explain the random variation that appears.
Humans evolved out of a common ancestor as monkeys did, so we are a kind of cousins with monkeys.
The missing link..
