If you are completely new to poker then there are many good resources around the internet that will take you through the game assuming no previous knowledge of poker.
- here is a good video introduction to the game, which runs to just under 10 minutes
- Here is another good web based introduction to the fundamentals of Hold'em Poker
Sometimes the best method of learning is to actually play; there are many online resources where you can watch and get involved in games.
- zyngapoker on Facebook is a lightweight version which is a gentle introduction to the game.
- PokerStars is one of the most well known sites for online poker. It has arguably the best software, a huge player pool and outstanding customer support. They also support a wide range of players at all levels.
- Other well known sites are PartyPoker and World Series of Poker.