The most popular Poker that you see lately is Texas Hold-em. This just means the style of play is different, but the rules to winning are the same. Poker is usually played with a five card hand. So, in order from the best hand to the worst:

Royal Flush - This means that you have the Ace, King, Queen, Jack, and Ten of the same suit. VERY, VERY hard to get! (Exactly, bet everything!)

Straight Flush - Means that you have cards of the same suit, but in order. Like having the 8, 9, 10, Jack, and Queen of diamonds or having the 2, 3, 4, 5, 6 of hearts. Again, VERY hard to get!

4 of a kind - Four of the same cards. For example, four tens, four Jacks or four two's. (Different suits, of course)
If two people have four of a kind, they get rated with the Ace being the highest, followed by King, then Queen, all the way to the two being the lowest.

Fullhouse - This just means that you have three of the same cards, plus a pair. For example, you have three six's and a pair of Aces, or three Jacks and a pair of Tens.

Flush - This just means that you have five cards with the same suit, but no order. Like if you have 2, 5, 10, Jack, and Queen of clubs. (If they were in order, that would be a straight flush.)

Straight - You have five cards in order, but not of the same suit. Like 4 of hearts, 5 of diamonds, 6 of clubs, 7 of diamonds, 8 of spades.

Three of a kind - You only have three of the same cards, like three 7's or three 5's.

Two pair - Just like it says, you have two pairs. Two 2's and Two 8's, or Two Aces and Two 9's.

No pair - If no one has anything, the winner is determined by the highest card in their hand. For instance, one hand has Ace, 10, 7, 5, and 2. The second hand has a Jack, 9, 7, 6, and 4. The winner would be the first hand, because it has an Ace. If both hands have an Ace, then the second card is compared, and so on and so forth.

As you can see, the trick is to play the odds of trying to get a better hand. The better the hand, the harder it is to get. The rest of Poker is all about betting on what you have in your hand and bluffing. Bluffing means pretending you have a good hand when you really don't. I'd tell you more about "bluffing", but that's an entirely new and huge topic.

First learn these rules. The art of bluffing is something that I'm sure a lot of people will have something to say about.