Timmy = the big guys. Big effects, big creatures, big cost for them. Examples of timmy cards are BFM or any creature with power/toughness of over 5/5. Newest addition to that is door to nothingness.
Johnny = combo cards. Things that make combos. e.g. intruder alarm
Spike = the tourney stuff. You know ravager, black lotus (any of the power 9, for that matter), entomb, etc. ... SKULLCLAMP! lol
These are the 3 types of magic players/cards that you'll run into. Almost all cards have one of these categories (with the bare exceptions of stuff like eagar cadet...lol).