cycling is basicaly the process of getting your tank stable, kinda like wolfman and striker mentioned , the reason it is referred to as cycling is because you will go through cycles or stages, which include a severe ammonia and nitrite spike which can and does kill many fish, that is why many of us sw LOVERS prefer to use either shrimp or lr and ls methods, the ammonia is highly toxic to the fish, some asay it is not inhumane, but basically you are putting your fish in poison whe this happens, so i have to say it is
anyhow the end result is your ammonia levels breeds bacteria which wil grow on everythign, the glass and sand adn rocks, thish bacteria breaks down your waste and keep s your water levels stable, this is known as your biofilter, which is highly effective much better thana ny type of filter you can buy, so these bacterias youwant, this is also why many of us prefer to not use a uv sterilizer, some like them, but most think that they kill way too much stuff in the water,
welcome aboard
HTH adn good luck