This should answer your questions about cycling the tank and when to add fish. Read through it and let us know if you need anything clarified.
http://www.fishlore.com/NitrogenCycle.htm
There are several different varieties of fish that are generally considered good "beginner" fish because they are hardy enough to survive common mistakes. Neons are not one of them. There are some other species that you might try for starters, then add the neons after you've had a month or two to learn, work out the kinks, and develop the maintenance routines needed for successful tank ownership. Some examples would White Clouds, Danios, platies, or mollies. Start out with a small school of 5-6 of one of these, learn the ropes, then add your neons as your confidence level rises. Just remember to research the adult size of the fish you put in your tank and do not put more than 1" of fish in per gallon of water. 20 gallon tank = 20" of fish. If you want to read up on those species, or others, here is a good place to start:
http://www.fishlore.com/TropicalFishProfiles.htm
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