Here's a breakdown of how natural selection works:

1. Variation: Individuals within a species have slightly different traits. These variations can be in their physical characteristics, behaviors, or even their ability to resist diseases.

2. Inheritance: These variations are passed down from parents to offspring.

3. Differential Survival and Reproduction: Some variations make an individual more likely to survive and reproduce in a particular environment. For example, a bird with a beak better suited for cracking seeds may be more successful in a habitat where seeds are plentiful.

4. Adaptation: Over time, the traits that lead to greater survival and reproduction become more common in the population, leading to changes in the species' characteristics.

Here's how books often explain the process:

* Darwin's Finches: Books frequently use the example of Darwin's finches, a group of birds that evolved different beak shapes on the Galapagos Islands, each adapted to the specific food source available on their respective island.

* Peppered Moths: Another popular example is the peppered moth, which changed from predominantly light-colored to darker colored during the Industrial Revolution. This adaptation helped the moths blend into the soot-covered trees, making them less likely to be eaten by predators.

* Antibiotic Resistance: Books often discuss the rise of antibiotic resistance in bacteria as a modern example of natural selection in action.

Important Note: Evolution is a continuous process, not a "goal-directed" one. Organisms evolve to become better suited to their current environment, not to become "perfect" or "more advanced."