A simple Google search using the phrase "What is a scrying mirror?" gives many resources to answer that question. I'd suggest the explanation at http://www.ebay.com/gds/How-to-use-a-Scrying-Mirror-Magick-Mirror-/10000000009366585/g.html as being pretty comprehensive.
And if you want to know how to make one, then why do you say not to send you a link that shows how to do just that?
But from the link at http://paganwiccan.about.com/od/samhaincrafts/ss/ScryingMirror.htm Here are instructions for making one.
To make your scrying mirror, you'll need the following:
A clear glass plate
Matte black spray paint
Additional paints (acrylic) for embellishment
To prepare the mirror, first you'll need to clean it. Use any glass cleaner, or for a more earth-friendly method, use vinegar mixed with water. Once the glass is clean, flip it over so that the back side is facing up. Lightly spray with the matte black spray paint. For the best result, hold the can a couple of feet away, and spray from side to side. If you hold the can too close, the paint will pool, and you don't want this. As each coat dries, add another coat. After five to six coats, the paint should be dense enough that you can't see through the paint if you hold the glass up to a light.
Once the paint has dried, turn the glass right side up. Use your acrylic paint to add embellishments around the outer edge of the plate -- you can add symbols of your tradition, magical sigils, or even your favorite saying.
The one in the photo says, " Thee I invoke by the moonlit sea, the standing stone, and the twisted tree,
" but yours can say anything you like. Allow these to dry as well. Your mirror is ready for scrying, but before you use it, you may want to consecrate it as you would any other magical item.