Buy yourself a sharpening stone for a dollar in Chinatown. If your city doesn't have a Chinatown, get one or move somewhere civilized.
This is a "water stone" which means you put water on it while using it to float the sharpening dust off it. Some prefer an "oil stone" which means you put oil on it. Some stones are born oily. Once the oil is in there water doesn't work well anymore.
This particular stone has had some use so it's dished out in the middle. That makes it hard to hold the knife at the right angle. So we'll need to flatten it.
Actually it doesn't really matter for knives, but when you start sharpening plane blades you'll make a religion of flattening your stone.