If your tank is still cycling this is the reason why you have ammonia. It takes, on average, 3 - 4 weeks to cycle a tank. If you bought a tank within last few weeks, your tank is probably still cycling. And if you add fish to a tank before it has finished cycling, it's not a good thing. You'll have ammonia now and
nitrite later on as the cycle progresses, and finally
nitrate. If you haven't read about the
nitrogen cycle, please do so now - it's in the Beginner's Articles on Fish Lore. Then you'll better understand why you have ammonia, etc. Even smallest amounts of ammonia and nitrite can kill your fish, so as long as you're getting any of these two compounds, change the water DAILY. If you don't keep removing these toxic compounds until the cycle is over, your fish may not make it, or may make it ending up very sick. So continue with daily water changes (say, 50%) until BOTH ammonia and nitrite = 0.
It's not that you're a bad fish keeper - most beginners usually don't know about the cycle and that's why they often end up with dead or sick fish. Besides, fish-keeping is much harder than caring for a cat or a dog.