Well it should have a yeasty smell. One possible problem is that watermelon wine is one of the hardest to get to ferment before it spoils. Hard to know how much actual watermelon might be in that juice.
But I would give up just yet.
OK - just looked at that page and I see a lot issues ( Outright WRONG info) issues there. Safest bet is to go to some site other than the sites that try to oversimplify.
Wine making isn't super hard but sites like that can scare more people away from wine making than encourage. This site a several other that are dedicated to winemaking will keep you out of trouble.
You can't really get started in wine making without some basics including some basic equipment. $20.00 - $50.00 is not really going to get you very far.
Look for a basic starter kit - most come with the basic chemicals/additives you need to safely make a good wine that won't gag you or turn into vinegar is a couple of week.
I started with this kit and I've added another $250.00 of hardware like carboys and bottling supplies etc. BUT you can get started for under $100.00 and do some decent wine making especially if you have access to fresh fruits. You can even use some store bought juices like the Welchs grape concentrate. In fact my favorite wine now is Pineapple Mango and that can be done from concentrates and a bag or two of fresh frozen mango chunks.
Don't give up. Just do some more reading on this site and perhaps ones like this one.
http://winemaking.jackkeller.net/index.asp