The real marvels are the ones where they graft apples, oranges, etc together. Expensive as hell and they don't survive as long though.

Take a small branch of a tree you like, splice it using a technique, take a small young tree of same type but different variety, splice it, attach branch of variety you like, seal. Nurture it, and the branch uses the donor tree to pull up nutrients and water, and the branch then grows into a whole new tree. It's cloning, but grafting helps it move faster and without as much risk.

Any branches you don’t remove will still be the original tree. You can have a single tree that yields multiple varieties of apples.

Yes but that's because the nursery has already grafted the branches of a known-to-be-tasty cultivar onto that tree before putting it up for sale.