In a 3 gallon tank, you are facing a 30% water change every few days at first. The water change will be made using water about the same temperature as the tank water and it will be treated with a dechlorinator. Most of us use Prime because it is cheaper to use in the long run. You will need a larger container eventually. 10 gallons would probably work. By the time you get a tank, a filter for it, a heater and thermometer you will be wondering if this was such a good idea because of the cost. The next thing you will need is a good liquid reagent based test kit like the API master freshwater test kit. You use the kit to measure ammonia, nitrites and nitrates. At first you focus on the ammonia because the water changes needed to keep that below 0.25 ppm will take care of everything else. When it starts to get easier, you test for nitrites because they will be rising and will start to determine how much water change is needed to keep them under 0.25 ppm. When the nitrites start to become easy to control or control themselves, you start testing for nitrates so that you will know how much water needs to be changed how often to keep things under 40 ppm of nitrates. That test never does change because if everything else has been done right, the nitrates are being produced from the ammonia by way of being nitrites. There are bacteria in the filter at that point that are converting ammonia to nitrite to nitrate. The ammonia is coming from the fish and from any fish food that was not eaten.
For a better and more complete description, there is a link in my signature area to "fish-in cycling"
Since many of the components you will need are much cheaper on line, you will also get familiar with using the internet to do some shopping.
