What are the positions?
There are 4 positions in poker to be concerned about. It’s based on where a player is seated relative to the button. The first third of seats from the left of the player with the button are called early position. The next third are middle position, and the last third are late position. The final position is the button itself. These are of increasing strength, with the button being the strongest position of all. The final position to note is the player who has to bet first, which is called being under the gun. It’s all based on the order of play. Simply put, those who act later are in a stronger position.
How much do these really matter?
A lot actually. How much is difficult to quantify. Unlike hand strength, with strictly mathematical odds of winning, positional strength is about using a chance to read your opponents. It isn’t possible to put a simple number on it.
Why do they matter?
In all but the first round of betting, the player on the button will get to watch the actions of every other player before they act themselves. This allows them to gain information about which players have strong hands, and how many, and how those hands have changed in response to new cards. It also allows for a bit of blind stealing, which is when a late acting player bets just to take the blinds, having already watched everyone before them check through the round. It’s a lot more dangerous to attempt in an early position, because it has to be done blind, and it’s easy to walk into strength later in the table without having had any indication that it was coming.
Playing position is done by taking your position into account when determining whether it’s time to bet or fold. In general, it means that you should fold or check a week hand when in an early position, but consider a hand stronger if you’re in a later position. A hand with T9s (Ten and Nine suited) is a weak hand in the early positions. Betting this hand risks losing quickly to a higher pair. From a later position, you can see how much strength is out there before deciding. T9s is drawing for pot odds anyways, and pot odds (or simply the amount of money in the pot divided by the bet needed to call it), are a lot easier to calculate when the betting has already happened and the pot is in front of you to count.
Later position can also be used to raise from. If a player seems to have a decent hand, and has bet it, you can look at the board and determine whether you have a stronger hand, and raise them. They didn’t get to see anything you were doing before this happened. That’s playing with power.
What are the positions?