How does sexual reproduction increase the genetic diversity among a population

In my opinion I feel that because when two human beings create another they share their genes with the new human being. As that human grows up it does the same thing. It's known as a cycle. I'm guess that there will be a time where two healthy people will decide to reproduce and will create a healthy baby. Although I'm not all sure.

I hope I explained well enough. xD

~Noodles~