Here's a demonstration of sharpener:
I also use a sharpening steel to keep the knife edge straight every time I'm about to cut food:
I've tried a few different kitchen knife sharpeners (including this Cook's Illustrated recommended sharpener) and my favorite is the KitchenIQ Edge Grip 2 Stage Knife Sharpener. It's only $6 on Amazon, but it has held up splendidly since I bought it in early 2015. It's got a corner-shaped groove that fits into a kitchen counter edge, which prevents slipping. It gives my favorite cheap kitchen knife (the $12 Winco Acero 8-inch chef's knife) a keen edge. I use the coarse sharpening groove (I can see tiny shards of metal coming off the knife) if the fine groove isn't doing the trick.
Here's a demonstration of sharpener:
I also use a sharpening steel to keep the knife edge straight every time I'm about to cut food: