What the difference of selection and variation?

Selection or 'Natural selection' means that the organisms that are better adapted to their environment are most likely to stay alive and produce offspring, while Variation means that during natural selection, the organism that is better adapted to the environment starts to form more physical features to help it survive (mutations).

For example,

Say that there was a white desert. If there were 2 mice, one species is black while the other is white, white would survive, which would be an example of Natural Selection. Variation is if, say, the mice are slow and can still be easy prey, but later on they mutate into becoming faster, that would be variation.