Old-fashioned rolled oats, quick oats, and steel-cut oats (also called Scotch oats, pinhead oats and Irish oats) are all the same basic ingredient-- whole oats-- cut and rolled differently.
Steel-cut oats are not rolled into flakes; they are cut into pieces (usually thirds). They take about a half hour to cook, depending on what consistency you're looking for.
Old-fashioned oats are made from steel-cut oats that are rolled to make them flat. They cook faster than steel-cut oats.
Quick-cooking oats are also rolled flat, but they are cut into smaller pieces so they cook faster (usually in about one minute).
For nutrition information and recipes for oats, see Superfood: Oats.