For a quick jump, you can see on the chart below made by Steve Bottorff described on his popular book Sharpening Made Easy: A Primer on Sharpening Knives and Other Edged Tools. The book tells many things about knife sharpening, sharpening system and DIY guide how to sharpen razor-sharp edges. If you want to surf deeper into the world of the sharpener, then it is one of a must-read book for you. For you who dwell in the Mainland or around the United Kingdom, you can buy the book through the link below.
Diamond plates are available in various plate sizes (from credit card to bench plate size) and grades of grit. A coarser grit is used to remove larger amounts of metal more rapidly, such as when forming an edge or restoring a damaged edge. A finer grit is used to remove the scratches of larger grits and to refine an edge. There are two-sided plates with each side coated with a different grit.