Evolution occurs when genetic mutations are inherited from the parent and passed to future generations.
Evolution is merely genetic mutations (both the good ones and the bad ones), once having occured, being passed on to successive generations.
Over time, those who inherit the beneficial mutations (which, by now are not considered to be "mutations") survive whereas those who don't inherit the beneficial mutations die out.
Examples of beneficial mutations are:
ability to see better
ability to run faster
ability to hear better
ability to stand up (required extensive changes to pelvic structure... more later).
None of these changes occured within one generation. Those with the beneficial mutation passed it on to their progeny, and over time the benefit became more pronounced.
Evolution is happening right now.
Farmers have been using evolution for thousands of years to breed new and better farm animals and crops. The corn we eat today is very different than the corn that was raised by the ancient Egyptians. Today's cattle are very different from cows a few hundred years ago. The difference is that farmers controlled the breading to select the best individuals and to cause them to reproduce instead of the inferior ones. We have taken control of evolution and used it to our benefit.