Through natural selection, the traits that are most likely to be passed on to succeeding generations are those that contribute to how helpful they are to the species based on environmental factors. For example, humans evolved to have fingers because they proved to be useful for climbing, grabbing, and a bunch of other things that were necessary to survive. So, those organisms that had that advantage ended up surviving and passing on their traits. In other words, natural selection is when an organism ADAPTS (inherits a characteristic that increases its ability to survive) to its environment and lives to pass on its traits. Think of the term "survival of the fittest." Hope this helped and I didn't confuse you too much! :)