Welcome to FishLore

That's the exact same thing we were told when we first started.
Unfortunatly, we didn't find Fish Lore until about a year after we had a tank of dead guppies.
Your fish aren't doomed and we'll try our best to help you and your fish through the cycling process.
First, you'll need a test kit. The API is highly recommended. Try to avoid the strips as they can be inaccurate.
Here's a basic explanation of the nitrogen cycle:
First your ammonia (from fish waste and left over food) will rise.
In a few weeks bacteria will start to develop and you'll see the nitrite levels rise and the ammonia levels start to drop.
After a few more weeks a different kind of bacteria begins to develop and you'll see the
nitrate levels rise and the nitrite levels drop.
Ammonia and nitrites are toxic to your fish.
So until your cycle is complete, you need to keep the levels down with 50% daily water changes.
Using Prime as your water conditioner will detox the ammonia for 24 hrs between water changes.
When you having readings of 0 on both ammonia and nitrites with some nitrates showing, your cycle is done.
Hang in there and be patient, cycling can take up to a month.
Best of luck.
