Low Grit Stones: A sharpening stone with grit number less than a 1000 is generally used for knives and tools that are damaged. If your blade has any nicks or chips in the blade, the stones will take care of them in a jiffy! They usually have a coarse side for nicks and chips, with the other side for general sharpening. Even if the knife’s edge has become totally blunt, the stone will re-sharpen it perfectly.
The basic concept of sharpening is simple – you're using an abrasive edge to remove metal – but the knife you buy may alter the method you should use. A general rule of thumb is that a waterstone can be used for both Japanese- and Western-style blades, but you should avoid pull-through sharpeners for Japanese knives (or any knife with very brittle blades).
The 6000 grit is great for having a nicely polished edge, it's the last step stone that I use for my knives in the kitchen. I like the King stones in general, they're a really good value and last much longer than the discount/cheap water stones. I use these stones to keep all of my kitchen knives nice and sharp and haven't had an issue with these stones. I also like that these soak quickly, I let them soak for about 10-20 minutes and they're ready to use. I have to flatten these a little more often than more expensive stones but I knew that was probably going to be the case when I bought them.
The grit range is important only in regards to the type of knives you will sharpen. It is entirely up to the consumer and how they utilize their knives. Obviously you want a stone that is capable of sharpening all your blades to the appropriate sharpness. As a rule of thumb, the higher the grit, the more you will be able to get the finest razor's edge. However, this might mean several more swipes back and forth along the stone, which can be quite time consuming.
If you’re sharpening high quality knives, you probably don’t want to use a cheapo sharpening stone. But if you’re just getting started with sharpening your pocket knife, there’s no need to get too fancy right off the bat. You can find a sharpening stone at most hardware stores for about $10. This one is very similar to the one I use. Nothing fancy. Most basic sharpening stones come with two sides: a rough grit and a fine grit. The finer the grit, the finer or sharper you can get your blade. You usually start off sharpening on the rough grit and then finish sharpening it on the finer grit.