Snakes have tiny hind leg bones, indicating that they likely descended from lizards.
vestigal structures are basically parts of any organisms body that currently arent being used anymore. this relates to evolution because these body parts used have a purpose, but as time went on and the animals evolved, they didnt need that part of their body anymore so it became useless.
for example, ostriches have wings but cant fly. in the past they were able to fly, but they evolved and dont fly anymore, so their wings became vestigal structures.