Don't buy short stones. It takes a long even stroke to put a even edge on tools, even chisels. At Freindship, Roger Needham is always set up near the main gate, with a table full of good stones for very reasonable prices. The black arkansas stone has been mined out, but he has a few small stones left, and has long stones made from quarried stone that is grey green in color, or even redish, that are about same fine grit size. A good 10-12 inch stone will serve you well the rest of your life. And it will cost you less than $30.00. While you are at it, you may want to buy another long stone in medium, or " washita" grade, to help you sharpen really dull tools.
I don't recommend using any oils on stone, as they make the steel slip over the stone, rather than allow it to be cut by the stone. Makes more work in sharpening tools. I use Liquid Wrench, or any other of the kerosene based fluids sold to help you break loose a stuck screw, such as " Break Free". I use this over oil because the oxydizers in the Liquid Wrench help break the hold on the bits of steel that clog the surface of the stone, so they can float up in the liquid and be wiped off. If your stone gets clogged with steel bits, the edge will slide off the stone, and the stone cannot cut it.
If you have never been trained in sharpening knives, or chisel, you always push the blade into the stone, as if you are trying to slice off a thin layer of the stone, to sharpen the edge. Then you must use a strop, made of leather or some very tough fiber, to remove the burr, or feather than is formed on the edge as a result of the sharpening process. Strop is done with a back stroke.
DON"T use a circular motion to sharpen tools, This tends to wear the center of the stone down into a dish shape, and you will soon not be able to get an even, and straight edge on any edge, and will either have to have the stone re- ground, or get a new one. Take long strokes from one corner to the opposite corner at the other end of the stone, Count strokes, Turn the stone around and use the other corners, all to keep the stone as flat as possible over the years.
I use a leather belt looped over a door knob to strop my edges; other glue a strip of leather to a flat piece of lumber, and use that to strop their tools. The smaller strop is adequate for short edges. I started using a belt for a strop when I was making knives 46 years ago, and I can use the belt to strop my chisels when needed, too.
Finally, I must recommend you buy a copy of the Razor Edge Book of Sharpening. It is the best book on the subject still around, and will save you hours of frustration in your work by helping you keep all your chisels and carving tools, knives, axes, etc. with razor sharp edges. The Razor Edge Company, in Eli, Minn. sells jigs to hold blades and chisels at defined degrees of angle for sharpening, and may be worth having if you are doing a lot of workworking with chisels. Cutting across the grain requires a very sharp edge. Knowing how to keep your tools sharp takes most of the work out of the work!