Paravanes are used  to set a lure or a usually live bait down to a certain depth when trolling. it is a rather advanced fishing technique, you would be best to stick to the basics for now.

ou can get a very basic one which has a small lure on it and is attached to a hand line, i have one and use it for catching Kahawai to use as live bait for kingfish.

If you picture a paper dart, it is the same as a paravane. The line is attached to the nose, the nose also has a weight on it so when it is in the water the nose points down and causes it to dive down. Mine then has a shot lenght of line with a kahawai lure attached to the back. This means when the Kahawai grab the lure this put weight at the back of paravane (dart) and causes it to rise up to the surface. 

They are great for kahawai workups or when you just miss the work up and the kahawai have gone deeper, you can toe it around behind the boat and get the lure down to mid water rather than on the surface. If im by myself i just chuck it out the back and watch for the paravane to surface and pull the fish in.

These are pretty cheap, around $20. So if you want to catch kahawai out of your dingy id say give it a go. As smudge said they can pretty complicated if you want to use bigger flasher versions for setting livies for marlin etc.

Heres a very basic one which i have

http://www.baitsdirect.com/acatalog/paravane.jpg

just found 1 looks bit big but i dunno

http://www.trademe.co.nz/Sports/Fishing/Big-game/Lures/auction-282495009.htm

cool u reckon i should get 1

there are many types of paravanes, there were called japanese surf boards, check out gourocks they have small commercial ones, the are used to tow lures the idea is simple, to set they go in the water upside down and tow deep, when you get a shot [bite] they fip over and plane to the surface towing the bait with them, the faster you go the deeper they get but then they become unstable and trip anyways, they are great towed behind the boat with a small feather jig on them. hope that may help you.

good stuff might give one a go