Cindy, someone would need to examine your Dremel Stylus in order to know exactly what is wrong. It may not be the capacitor, why do you believe it might be the capacitor?
If your Dremel Stylus is still under warranty, you should return it to the store from where you bought it, or, if you bought it on-line, you should contact the retailer who sold it on-line and ask what to do next.
Does your stylus plug into an outlet when you use it? Or is it cordless?
It may be that the battery has finally died.
Capacitors are used in a range of devices but there is a very special type of capacitor that is used with corded appliances to start a motor turning and a different capacitor to keep it running. Motor capacitor
Until it can be determined exactly what is wrong with your Stylus, no one will be able to give you exactly the help you need.
Have you checked the fuse in the plug? Also, have you checked if the Dremel runs in a different outlet?
If you plug it in and adjust the speed control and listen carefully, does it hum at all? Or is there no sound at all?
When you have finished with it, do you put it away? Do you wrap the cord around the base? Could the cord have been damaged? You need to carefully feel along the length of the cable until you reach the end or you reach a point in the cable where it does not feel the same.
Hold up the cord and loop it loosely between your thumb and first finger. Make a loop about 3 inches across. move the cord to make a fresh 3 inch loop. If at any point the curve in the loop looks a bit pointy, the cord may have failed.
There are so many things that could go wrong.
As you have mentioned that you do not know what a capacitor is, it may be a good idea to take it to a repair shop. Ask them for an estimated cost to repair and to tell you what happened. They should not charge you for an estimate. If they do, it should only be a small amount. 5-10.
I have successfully repaired several Dremels but I am an electronics graduate.
If you find out what the repair shop suspect might be the problem, come back here and post more information.
If I remember correctly, you will probably need a special Torx splined screwdriver to open the case if the fault is inside. Don't buy anything just yet. And don't go to just one repair shop, try two or more. If they all say similar things for the fault, then we can sort this out.
Hope this helps.