Mutations and natural selection cause adaptations. Mutations can cause instant adaptations, while natural selection is the process by which adaptations occurs over a series of generations.
Adaptations are changes or processes of changes by which an organism or species becomes better suited for its environment.
A mutation is an alteration of the DNA sequence. Sometimes such alterations code for the same amino acid sequence as the unaltered DNA strand during protein synthesis. In such a circumstance, the mutation is not detectable. However, other mutations alter the genetic code in such a way that a noticeable change in the trait that is associated with that gene is visible. Sometimes such mutations are advantageous and improve the organism's ability to survive in its environment.
Natural selection is the process by which organisms with more advantageous traits (being camouflaged, being covered with the correct outer covering for the temperatures of that environment, stronger/ larger/ or faster to fight off or run from predators, etc.) are more likely to survive in a particular environment. Likewise, organisms less advantageous traits are more likely to die due to the pressures exerted by the environment (such as temperature, predators, illness, etc.). Therefore, the organisms with the advantageous traits that survive are more likely to survive to find a mate and reproduce. Thus, the advantageous traits are passed down to future generations.