Cribbage is a 17th-century English card game that requires a board to keep track of the scoring. Learning cribbage is mostly a matter of learning the arcane scoring system.
Scoring happens in three phases:
1. Scoring during play
As you and your opponent play cards, one at a time, you can score points based on certain combinations of your cards and your opponent's cards. For example, if your opponent first plays a King (which has a count value of 10) and you play a 5, you have brought the count to exactly 15, and so score two points on the Cribbage board.
You can also score points by playing a third card to create a run. For example, if cards played were 9 and 7, you can play 8 to make a run for three points. Each card in a run scores one point. The cards do not have to be in numerical order, but they must be played one card after the other without breaking the run.
Here's another good example of a run where the cards are not in numerical order. The cards played are 2, 6, and 4. Playing a 5 scores three points for a three-card run. Now the cards are 2, 6, 4, and 5 with a count of 17. If you play a 3, then it's a run of five cards and scores five points.
It is also possible to play a seven-card run. For example, if the cards played were Ace, 2, 3, 4, 5, and 6, you can play a 7 to make a run. Ace, 2, 3, 4, 5, 6, and 7 equals a count of 28. With a seven-card run, you will get one point for each card, for a total of seven points.
When you are scoring your hand, you include the starter card, if it is to your advantage. The starter card can be used to get you more 15s or runs, but it isn't ever used to hurt your hand, to break up a flush, for example. If your four cards are all Hearts, and the starter card is the 9 of Clubs, you still get points for a flush. If the 6 of Hearts is in your hand, you can still add that to the starter card and also get a 15 for two more points.