A sharp knife is essential for cutting anything when you're cooking.
You can buy a sharpening stone, I have one that has two sides, one for putting the edge on and the other is smoother for fine honing. A steel is for truing up the edge while in use. The steel doesn't actually sharpen, when you use the knife the fine edge bends over and makes it seem like it's gone blunt, you'd need a microscope to see it. It hasn't, the steel just straightens up the edge again. as DT said, always cut away from you and keep your fingers out of the way!