How does someone become a world class athlete? How are they chosen to be in the Olympics?

To answer the overall research question I will try to find out.

1.Are athletes born or created?
2. How do athletes train for these sports?
3.Are most athletes real or do they use performance enhancements?

This is what I already know about this topic, I want to find out:
I know that many of the worlds best athletes compete in the Olympics. But, I am wondering if these athletes have trained so hard to get their or do they have natural talent? Also, do the most successful athletes work hard or use performance enhancements?