A diamond loupe is a small hand held magnifier used to look at diamonds and gem stones to determine the Quality of the stone. A standard loupe will  have a 10x magnification.  It will make what ever you are looking at look ten times larger. That way, you can look at all aspects of the diamond or gem stone from the outside of the stone to determine the quality of the cut and finish ,or what is inside the stone to determine its clarity or any internal imperfections. Step one is practice with the loupe. Make sure that you are in good light.  If you wear glasses it helps if you take them off.  Take the loupe in one hand and bring it very close to your eye. Not so close that you touch your eyelashes, but almost. Now bring your thumb up to your eye until it starts to come into focus.  Do not move the loupe, only move the item you want to look at. It helps some people to close one eye, but it is not a must. When your  thumb is in focus and you can see it clearly, move it around very slightly and look at the different areas. When you are ready find other small items to examine. REMEMBER move the item into focus, not the loupe. Now take the diamond  and bring it into focus. Once you see the tips of the prongs that hold the stone don't bring it in any closer. Move the stone around and look at all sides of it for any imperfections (any chips or scratches on the surface).  Now bring the stone closer and what is slightly under the suface will come into focus. Bring the stone slightly closer still, and you can look deep into the stone.  Make sure to look for anything  inside the stone. Don't be fooled  by a reflection  of a prong some times they look like imperfections inside the stone. Turn the stone upside down and see if is still there or if it has vanished. The best thing to do is PRACTICE, PRACTICE, PRACTICE. Now your a pro!