Describe the relationship between variation and natural selection

Natural selection is when certain characteristics cause a species or an individual to survive. Specific genetic defects might make survival harder for an animal or living thing, such as a missing or deformed limb might make an animal not capable for things like hunting or something like that.

As variation, I am not too sure. But I would assume variation could mean (example) there are many butterflies, but there are different types, or variations, of butterflies

Hope this helped