"Put that in your pipe and smoke it."
You can either smoke it alone, or with weed. Smoke a bowl or two of it without weed. If you get a good buzz, then it's hash. If not, then it's fake.
If your dealer told you to "smoke it on top of weed" you've probably been scammed.
Smoking it on weed is a good way to smoke it though, don't get me wrong.
Also, you can mix it with weed, and roll a joint with it.