What is natural selection?

The process whereby organisms better adapted to their environment tend to survive and produce more offspring. The theory of its action was first fully expounded by Charles Darwin and is now believed to be the main process that brings about evolution

How did humans evolve?    

 Since the earliest hominid species diverged from the ancestor we share with modern African apes, 5 to 8 million years ago, there have been at least a dozen different species of these humanlike creatures. Many of these hominid species are close relatives, but not human ancestors. Most went extinct without giving rise to other species. Some of the extinct hominids known today, however, are almost certainly direct ancestors of Homo sapiens. While the total number of species that existed and the relationships among them is still unknown, the picture becomes clearer as new fossils are found. Humans evolved through the same biological processes that govern the evolution of all life on Earth.  

Is there evidence for evolution? 

In the 150 years since Darwin proposed the theory of evolution by natural selection, a mountain of evidence has accumulated to support the theory. A greatly expanded fossil record since Darwin's time, the discovery of DNA and the process of genetic replication, an understanding of radioactive decay, observations of natural selection in the wild and in laboratories, and evidence in the genomes of many different organisms, including humans, have all bolstered the validity of the theory of evolution.