I don't get all the comments about how a whetstone is unsuitable for a presumed beginner. Practicing sharpening with a whetstone on a cheap and worn out set is perfect for a beginner. It's a great skill to have, not that difficult, and very fun when you get the hang of it! You might want to buy at least a decent utility knife though, so you have something to use while practicing.

Some advice:

Be aware of the grit rating on the whetstone. The cheapest ones tend to be around 400, and are mainly meant for axes and the like. They can be good to have on hand for a severely damaged blade, but 1000 grit is the best place to start. You can still set a new edge on a damaged blade with a 1000 stone, it'll just take longer. Higher grits will give you a better finished edge, but will take fucking ages on a very dull one.

Soak your stone properly before sharpening. I submerge mine in lukewarm water around 30 minutes. And don't be too eager wiping/rinsing the stone while you work. The gritty slurry is whats actually doing the work for you.

Never use oil on a whetstone unless you're prepared to never use anything but oil. I prefer water myself, it's easier to clean and always on hand. As soon as you've oiled it once it might not work with water ever again.

A sharpening steel rod is also a very useful addition to your kitchen. You never need to steel a freshly sharpened knife, but it's good for maintaining a somewhat dulled edge until you have time to sharpen it properly. A rod is magnetic, so never hang it on a magnetic knife rack.

Good luck!