If you want to try it, then download it from the Internet as anyone will just ban you from their game if you're downloading because noone likes newbies.
Also, if you do bad, expect to be put on a banlist program. If you do good, expect to be put on a banlist program by sore losers.
Unbalanced heroes. No skill whatsoever. Memorizing may be a skill in some games, but memorizing item orders is way too easy anyone can do it.
Search DotA on Youtube, there's probably vids of it. Also League of Legends is like it, and there are a few other commercial games like it. Basically, you pick a hero, grind on random weaklings sent to your base, buy items, kill heroes. You try to destroy the enemies base.