Not quite. Evolution is the process of descent from a common ancestor. Extinction explains fossils of species no longer seen living on Earth. Evolution explains the presence of species that appear in the fossil record at various times.Evolution is the theory that species evolved from each other, which explains fossils of species no longer seen living on Earth.
Again, not quite. Populations consist of a variety of slightly different genes in various proportions in that population. If the environment changes and forests disappear, forest animals that can survive on a savannah will reproduce and the gene pool of that population will be changedVariation: while most offspring will be very similar to their parents, occasionally an individual is born/hatched/seeded that has a slight or significant difference. For example, an animal similar to the giraffe, but with a much shorter "normal-sized" neck, might give birth to a mutated calf with a longer neck.