Very carefully. I'm actually a bit of a holdem addict so I try to stay away as much as I can otherwise I start fiending again,
For holdem, you are dealt 2 cards. If youve ever played Poker, the rules are the same. Try to et the best poker hand with what you get. You place ur bets by the cards u are dealt and once a round of bets go through, the next 3 cards are dealt face up on the table. Those are shared with all players that are still in the game. Once again, you go around the table, Check, Bet or fold. A 4th card is dealt face up for all players....and same thing. Check, bet or fold. The final card is dealt face up and this is where it gets fun.
The player with the best hand using one or 2 of their "pocket" cards (the cards they were dealt originally), also using up to 3 face up cards, wins. Kinda hard to explain over the forums, and is best to learn in person. The best place I have found to play is actually:
www.fulltiltpoker.com You can DL the game there and play for free (or even add ur CC and pay for real, but its better for free so u dont "bet the house"! lol. Hope that helps.