If it is uncooked you need to boil them in their skins for about an hour and a half. Peel them.then cut into thin slices and cover with vinegar .brown is best. Wear a plastic glove or put your hand in a plastic bag as they stain .
My mum used to cook beetroot, slice it, add some sliced onions & cover with vinegar. It would keep for days in the frdge & the combination of both was lovely.