If you're curious about the differences between groats and oats -- instant, quick-cooking and rolled -- read on.
Oatmeal is considered a whole grain, but oat groats are the most natural, least processed form of oats. Only the hull has been removed. When you buy steel-cut oats, you're buying groats that have been cut into tiny bits. These are lovely cooked into porridge. They are not suitable for making muesli or granola, however.
The big Quaker canister holds rolled oats. They are still whole grain, but they have been steamed and rolled into flat flakes so they cook more quickly. Old-fashioned rolled oats take longer to cook than "quick oats," which have been more thoroughly flattened, but the old-fashioned variety has more texture, which is a consideration if you are substituting quick oats for old-fashioned.
Instant oats have been rolled so thinly, they're often nearly powdered. They cook very quickly and have the least texture of all. If your oatmeal has all the appeal of wallpaper paste, you're probably using instant oats. Try old-fashioned oats or groats instead.