Gambling Man say;

The Pass Line that goes around the whole table and the Don't Pass Line that tends to mirror it are the two basic bets of craps.

The game starts with the shooter placing one or the other of these bets. Since most players are "right bettors," that is, they bet the Pass Line, let's look at the game from the perspective of the Pass Line. The shooter places a bet on the Pass Line. He is given the dice. The shooter now rolls the dice. If he rolls a 7 or 11, the Pass Line bettors win even money -- i.e., you bet $10, you win $10. The Don't Pass bettors lose. However, if the shooter rolls a 2, 3 or 12, the Pass Line bettors lose and, on the 2 or 3, the Don't Pass bettors win; while on the 12, the Don't Pass bettors push, neither winning nor losing

If the shooter rolls any one of the following numbers: 4,5,6,8,9, or 10; this number becomes the point. For the Pass Line bettor to win, the shooter must roll that number again before he rolls a 7. The reverse holds true for the Don't Pass bettor. If a 7 is rolled before the point, the Don't Pass bettor wins

That's the game, pure and simple.

Here's an example of how this option works:

The 7 can be made six different ways with two dice. The 4 can be made three different ways with two dice. Thus, the odds of a 7 appearing in relation to a 4 are six ways to three ways or two to one. Once the shooter has established his point number (let's keep it as the 4), the player has the option of placing an amount equal to (single odds), twice as much (double or 2X odds), three times as much (triple or 3X odds), five times as much (5X Odds), ten times as much (10X Odds), 20 times as much (20X Odds), or 100 times (100X Odds) or more, as his Pass Line bet in "odds" immediately behind it. Let's analyze the bet based on double odds

The point is 4 and you have $10 on the Pass Line. You can now place $20 in odds behind it. If the shooter rolls a 4, you will be paid even money for your $10 Pass Line bet and the true odds for the Odds bet -- thus, you would win $40 for your $20 Odds bet. The casino has no edge whatsoever on this bet in the long run. The Free Odds bet reduces the casino edge on the Pass Line as follows (the Don't Pass is fractionally less):

Two other low-percentage bets are the Come and Don't Come bets. These function in exactly the same way and have exactly the same house edges as the Pass and Don't Pass bets. The only difference is that they are made after the point is established. Once the shooter has a point, you can place a bet in the large Come area on the layout or on the smaller Don't Come area in the upper left and right hand corners of the layout. A 7 or 11 wins the Come bet at even money, loses the Don't Come bet. A 2, 3 or 12, loses the Come bet. While the 2 or 3 wins the Don't Come bet. Again the 12 is a push. However, should one of the point numbers be rolled (i.e., 4, 5, 6, 8, 9, or 10), that number now must be rolled before the 7 for the Come bettor to win. Should the 7 appear before the number, the Don't Come bettor wins. The Come-Don't Come is merely a game within a game. As with the Pass and Don't Pass, the Come and Don't Come players are also offered the option of Free Odds.