Basically what Perslos said, but I'll give you the tl;dr version.
Basically online flash games are made from a program called Adobe Flash. Basically to learn how to make games, you got to know how to draw with things like MsPaint, and the hard part is learning to script.
Script is simply a way to type out your commande in things called tags. Languages are very hard to learn, and therefor unless you are extremely dedicated, don't get into flash.
