Here's a breakdown:

* Alleles: Different versions of a gene. For example, the gene for eye color might have an allele for brown eyes and an allele for blue eyes.

* Frequency: How common an allele is in a population.

* Natural Selection: The process where individuals with traits better suited to their environment survive and reproduce more successfully, passing on those beneficial traits to their offspring.

How it works:

1. Variation: Individuals within a population have different traits due to variations in their alleles.

2. Differential Survival and Reproduction: Individuals with traits that give them an advantage in their environment (like better camouflage, faster speed, or resistance to disease) are more likely to survive and reproduce.

3. Inheritance: Beneficial traits are passed on to offspring, increasing the frequency of those alleles in the next generation.

4. Change in Allele Frequency: Over time, the frequency of alleles that code for advantageous traits increases in the population, while the frequency of alleles for less advantageous traits decreases.

In summary: Natural selection acts on the variation within a population, favoring individuals with advantageous traits and leading to a change in the frequency of alleles in the population over generations.