Hi Tanny and welcome to TFF!
We get dozens of beginners each week who are in the same situation, bad advice and about to lose their fish, so you've stumbled across the right place to be.
Unfortunately you're fish are probably in an emergency situation and the very first thing you should do is begin performing 50% daily water changes, assuming you haven't got a test kit and don't know what your ammonia and nitrite(NO2) readings are for the tank water. The way you perform a water change is to either use a siphon or bucket to remove water (in the future the members can help you learn how to do a gravel clean in association with this) and then prepare tap water to replace this partial water change. You want to use a dechlorination/dechloramination product, following the instructions for the amount. You also should temperature-match the water (roughly, your hand is a good enough guide.)
OK, so that's your first emergency assignment. Do that at least once a day until you can get a test kit. Meanwhile the test kit you need to find is a type with little bottles and test tubes. These tests, the ones based on liquid-reagents rather than paper strips are necessary to have enough accuracy for what you need. Many of us use the API Freshwater Master Test Kit, but if you can't find that, another good one is the Nutrafin Mini-Master Test Kit. The needed test are for Ammonia, Nitrite(NO2), pH and Nitrate(NO3) and that's the order of importance I'd place them in. Again, do not get test strips, they are worse than bad, they are misleading.
Once you get your test kit, follow the instructions carefully to test both your tap water and tank water and post up the results here in your thread. The members will need to see this for their further help.
Now the third thing, slightly less urgent but more fun is that you need to begin reading(about now you're probably thinking this is really weird, but believe me, you've really been extremely lucky, finding the best place possible for leaning the hobby in the best possible way and getting up to speed much more quickly than otherwise!!). Look here in the pinned articles at the top of our "New to the Hobby" forum under Beginners Resource Center and try to look particular at articles about the Nitrogen Cycle and about Setting up tanks.
It turns out that the filter (the real heart of the hobby) that they sold you is really just a piece of hardware that is meant to be used by a hobbyist, who somehow has learned about the hobby, and who knows what's involved in the arcane setup of one of these things! Its really not meant to be funtional for fish for at least about a month! (Local fish stores, as you can imagine, often feel its impossible to inform people of this and still feel like they're going to stay in business!)
Filters have three main functions: Mechanical, chemical and biological filtration. Mechanical filtration is removing debris and particles and is the only function that most people think they are meant for, thus the confusion. Chemical filtration is a special case and not needed under normal circumstances. Biofiltration is the big surprise for most beginners. Its one of the great secrets to good fishkeeping!
Unlike mammals, fish give of ammonia along with CO2 when they "respire." Also, in a fish tank, plant debris, fish waste and excess fish food are broken down in the water by certain types of bacteria and tranformed into... you guessed it, ammonia! In nature, this ammonia is diluted by vast quantities of fresh water. In aquariums, ammonia, in even small amounts will cause permanent gill damage and rapidly kill fish.
The "biofilter" we were talking about is an amazing device because we grow two specific species of bacteria in it and the first of these (the ammonia oxidizing bacteria, or "A-Bacs" for short) will "eat" ammonia and transform the nitrogen in the ammonia into another substance, nitrite(NO2). This nitrite(NO2) is also very dangerous to fish because it causes them to suffocate (it damages the hemoglobin in their blood) and get permanent nerve damage prior to dying.
The second of our two species of bacteria in the filter, however, will "eat" nitrite(NO2) and transform the nitrogen into nitrate(NO3), which luckily is much, much, less harmful to fish and can be removed with weekly water changes. That is a short version of how the modern aquarium biofilter works and understanding its importance is central to the hobby.
The situation you're currently in is what we call a "Fish-In" Cycling situation. We can't always save the fish but the members here are pretty good with these and can often coax you though the procedure and help you in the best ways possible. If you can't take the fish back to the store or re-home them otherwise, you'll have to keep this "fish-in" cycle going usually for about a month while the filter cycles. The way you tell if its cycled is if it can go two full days without needing a water change and testing zero ammonia and zero nitrite during your morning and evening tests on those two days. During a fish-in cycle you use your new test kit to do detective work and find out what percentage and frequency of water changes on your particular tank with your particular fish is necessary to keep both your ammonia and nitrite levels always below 0.25ppm and hopefully as close to zero as possible throughout the day and night. Depending on how much waste your fish produce (and you should feed lightly once a day or every other day), you may get by with 50% water changes a day or you may need more or less, it just depends on the testing.
Good Luck! ~~waterdrop~~
hi guy's
) (now that I think of it I think jonesyUK is a teacher, so appropriate to keep us up on these things 
