The first thing to learn about poker is the hand values.  Without this in memory, you are unlikely to win.  Its amazing how many home games I have been to and people have to check whether a flush beats a straight. 

This assumes a “high” poker game. There are some variants where the lowest hand wins.

Royal Straight FlushThe best hand in Poker. Basically a royal straight and a flush together. Ace, King, Queen, Jack and 10, all of the same suit.
 Probability. 0.0001539% (ie, less than 2 in a million)Straight FlushAny five-card sequence in the same suit (for example, 6, 7, 8, 9, 10 of clubs)
 Probability. 0.00139%

Four of a Kind

All four cards of the same value (for example, King, King, King, King).
 Probability. 0.02401%

Full House

A three of a kind and a pair. (for example, Ace, Ace, Ace with 7, 7).
 Probability. 0.14406%

Flush

Any five cards of the same suit. (for example, 4, 5, 9, 10 and Jack of spades).
 Probability. 0.20%

Straight

Five cards in a running sequence, but not in the same suit (for example, 7 of clubs, 8 of clubs, 9 of hearts, 10 of spades and Jack of hearts).
 Probability. 0.39%

Three of a Kind

Three cards of the same value (for example, 5, 5, 5).
 Probability. 2.11%

Two Pair

Two separate pairs (for example, 2, 2).
 Probability. 4.75%

Pair

Two cards of the same value (for example, 9, 9).
 Probability. 42.26%

High Card

If no one has any of the hands above the winner is the one with the highest card.
 Probability. 50.12%

 poker hand values

 

You can see that the higher that hand value the less likely it is to get.  For example a flush is about half as likely as a straight.