A glass cutting board will dull a knife very rapidly, since glass is harder than steel, and flattens the knife-edge (which is simply a wedge or complex wedge). That is why wood or plastic resin is used. The knife cuts into the wood or resin, rather than the resin flattening the knife. You get a tiny bit of wood fibers in your food -- harmless -- or a tiny bit of plastic resin fibers (less) -- probably not enough to cause one to need to worry about it.
You can dice maybe 20 carrots on a hard-maple cutting board before you need to sharpen your knife with a sharpening stone (also harder than steel, but it abrades the steel, rather than bashes it flat, relatively.) Less than one carrot on a glass cutting board will probably dull your knife. You won't be able to finish dicing one carrot -- your knife edge will become too dull to finish the job, unless you are using a serrated knife (the undercut areas won't contact the cutting board, only the tips will become dull).
To test sharpness, simply cut a piece of computer printer paper. It should slice thru the paper easily, without much "sawing." Just knick the edge of the paper, then push thru with one stroke. If the paper tends to rips instead of cutint cleanly, and requires back and forth sawing rather than goes down a few inches when pushed or pulled in only one direction -- then you need to sharpen your knife.
simply buy a cheap oilstone, put light oil (like 3-in-one brand) oil on it, then reshape your knife edge - this is hard to describe in words. Much easier to show. But basicly you just abrade the edge down on both sides evenly, to about the same angle that it was originally. 30 degrees total for the 2 edges (each plane 15 degrees from the plane thru the center of the knife) making sure you have created a "line of points," rather than a line of flat spots.