Problem:

I've been wondering lately how evolution manages to produce complex organs. It is pretty obvious to me how evolution would select some minor traits like size, resistnce to illness or climate. There is a mutation where some organisms are slightly different and better traits are selected. However I cannot imagine how an organism will mutate to have lets say lungs at once and unless organism has a functional organ there is no reason for the trait to be selected.

Question: How does evolution produce complex organs?

Question: Maybe the animal will feel hormonal changes that cause it to increase body heat to help her sit on the egg, etc.?

Please describe the process of evolution.