If you really want to have an aquarium out of this glass, I'd get a pro to do it, simply because cutting glass, while not especially difficult a skill to learn, has a learning curve, just like any other skill. You will make mistakes and you don't have a lot of glass to practice on.
But if you want to try it, and not getting a little tank out of it is not going to be a real disappointment to you, then yeah, try it. Glass cutting is a useful thing to be able to do.
The main thing is that you can only cut each line one time. Once you've run the cutter wheel down the glass, you cannot do it over again. Really what you doing is scoring the glass, making a shallow cut to start with. So you need that straight edge BillD mentioned, preferably clamped in place. Start with the wheel just off the glass, press enough to hear it, then go smoothly, evenly, after running a bit of oil or whatever to lube the cut, 'til you run off the other side. Press firmly but not to hard, that's something you can only discover by doing it.
If you do it right, you'll hear a high pitched sort of whine as you go. Once the score is done, you need to snap or break the glass along the score, there's a couple of ways to do that. You can rest the main piece on a bench or table with the scored line just over the edge and lean on the end piece 'til it snaps. Or place a pencil or dowel under the scored line on a table and press down on both sides of it. Tapping gently along the scored line first using the end of the cutting tool, before trying to snap the glass, will help deepen the score, and hopefully make it break nice and clean.
If the scored line is not straight or is uneven in pressure, you may end up either with an assortment of broken pieces or maybe just lumpy edges on your piece, like teeth. If the lumps are small you can sand them off, and to make a tank they need to be sanded flush with the main edge. You'll need an abrasive with a cloth back and a few grits to work through, the sort used for body work or metal, not wood. If you have to buy the abrasives, it will add a bit of cost and sanding down lumps is not as easy as just taking off the sharp edges. The pros can do it in seconds with their machines. There is also another type of tool for breaking glass and maybe tile too. I have forgotten the proper name for it, but it has flat gripping plates at the ends, and can be used to break off larger 'chunks' that may result from a wonky score line, or narrow pieces that you can't break the usual ways but then, you're investing that much more in tools you may never use again. If you get clean cuts, those snapping pliers are not needed.
But it's an interesting thing to do and with beginner's luck you may well end up with a tank for your effort. If you end up with most of the pieces right, buying one more to complete it won't be terribly costly. My local shop wants, I think it was $5.,for a piece of 5mm glass 7 X 8 inches in size. Your glass would cost a bit more, as it is thicker than 5mm.