First, just to reduce any confusion in the future, the light you have is a studio flash, or flash. A speedlite (or speedlight) would refer to a hotshoe mounted flash.
Yes, the flash is certainly usable with the 3100. You will, however, need a way to have the camera trigger it. The basic way to do this is with the sync cord, which came with the light, but you may not have received it, and it may not be good at this point anyway. We do sell replacements. If you go the sync cord route, you will need a hotshoe adapter. This provides a socket for the cord, which is not present on that model camera. We also carry these adapters.
Another solution is an optical triggering device (basically a hotshoe mounted flash). These can be a white light flash, like a normal speedlite, or one that has an infrared filter on it. We do not carry these, but you may already have a speedlite. If it can be set to M mode, it will work. The pop up flash on that camera will not work (to my knowledge).
The best solution, in the opinion of most people, is a radio remote system, like our CyberSyncs. This involves a transmitter on the camera and a receiver on the light. This will be the most expensive option, but is often the most convenient.
Also, if the light has not been used in a while, you may want to exercise the capacitors. You can do this by lowering the power to minimum and firing the light 10 times or so. Then move the slider up a stop, and firing 10 shots or so. Repeat this process until you reach full power. I would do this outside or in a garage, as a capacitor failure could smoke or drip, as well as make a loud pop.
As for using flash units in general,
http://strobist.blogspot.com/2006/02/we ... obist.html is a good site. This may seem like it is a speedlite based site, but the idea is to use what you have available, and the principles are the same.
We also have a "studio flash explained" section here:
http://www.paulcbuff.com/sfe.php