I am really pleased to see you admit that you don't understand. Its a lot easier to help you when you start out that way. Helping someone who knows it all is quite challenging.
Would you like to learn it?
Its not that hard.
Step one... go get some test kits. A cycled tank would rarely need to be tested for ammonia or nitrite, but a mature tank should be tested for nitrate, pH, KH and GH once in a while. Dip stick test strips are useless. A test that uses liquid drops in a test tube is what you want. API is my first choice, but there are other good brands as well.
This kit will do pH, ammonia, nitrite and nitrate. If you don't have plants the only other things to watch are
KH and GH. And those don't need to be tested very often. If you know some one that has a KH and GH test kit... share them, if not, spend the extra $6 and have them. The nitrite and ammonia tests are something that would get used on a mature tank in the even of an emergency, such as what you just experienced, they would not be needed often unless you were cycling a tank.
It would be my pleasure to walk you through a crash course in water chemistry if you want one.