These numbers refer to the VP$IP (voluntarily put money into pot) and PFR (pre flop raise) statistics players have gathered using tools such as Hold'em Manager or Poker Tracker. These tools are programs that mine data from your collection of hand histories and display any number of statistics you may choose on a heads-up display (HUD) while you play providing you with better knowledge about your opponents' play styles. A high VP$IP means the player is loose preflop, though it won't tell you much else. A high PFR means your opponent frequently raises preflop and is probably a more aggressive player.
So a 12/10 tag would be someone who is rather tight and usually agressive because most of the time they enter a pot, it will be with a raise. Normally these stats are enough to get you by in micro and low limit games. But you won't be able to develop a true read without more information and a large number of hands collected on any given opponent, which is especially important in higher limits where nearly every opponent you face will be using a HUD.