mcoccia,
you can use plain old scotch tape or packing tape to seal the gaps of you want to. Or use can use monokote (or whatever brand of covering that you prefer). Since this is your first plane it may be easiest to just use cleat tape to seal them up. It's pretty simple to do. Deflect the control surface back as much as possible (it helps to have a second person sometimes, or use tape to hold it back). Then fold you tape in half and put it in the gap. make sure you use something to work it down on both sides of the gap so that it's firmly attached (you don't want it bunching up in the gap), and then smooth the tops down. That's all you need to do.

I do want to clarify a little what I said earlier. I should have said that sealing the hinge gaps will not usually have any affect at preventing flutter. The other things I mentioned in my above post are what should be checked if you have a flutter situation. Sealing your hinge gaps will improve the performance of your plane by eliminating air leaking through the gap.

Hope this helps

Ken