If using fresh beets: Remove leaves, leaving about an inch of stem, and don’t cut the taproot. Wash gently (don’t break the skin), and place in a pot of cold water to cover. Bring to a boil and cook until done (firm but cooked, about 40-50 minutes). Drain the beets, cool under running cold water, and remove skin with fingers. Slice.
Combine beets, garlic, oil, and vinegar in a bowl and toss. Add salt and pepper to taste, and refrigerate covered for several hours before serving.