It is estimated that there are over one billion dollars wagered on sports in the United States each year. Probably around half of that is from illegal betting, since only two states allow legal sports betting within their state and one of those limits it severely.
Nevada is the only state where you can bet on just about any sport or any event legally. Casinos and Sports Books are privately owned and are famous for their lights, shows and extravagant amenities. Delaware allows only NFL parlay cards and the system is run by the state. No other state in the U.S. allows the placing of bets on sports in land based sports books.
The placing of online bets is a little more gray. Some states don't have laws against placing online bets. Some states have laws against accepting bets from that state, but not from bettors placing bets from that state to a location outside the state or county. And Federal laws don't usually match up with state laws.
There is no doubt that sports betting will be added over time to additional states. The most likely place to see these new ventures will be in states that currently have Tribal Casinos. It will only take one Tribal Casino to challenge the legality of it on their sovereign land and win to open the flood gates to more or all Tribal Casinos to get it. As stated above, there are multi-billions of wagers being placed that if they had a better option like a sports book, would do it in a heart beat.
The two main types of bets when it comes to sports betting are straight bets (also known as point spread bets) and moneyline bets. There are many other types of bets, but these are the two most popular and most basic bets available. When placing these bets, you are placing a wager against the sports book on a specific team, during a specific game. Your bet will be complete as soon as the game is over and you will either win, lose or tie with no other catches or links to other games.
Point spread bets are placed on a team, but the final score of the game is not what decides the final outcome of the bet. When placing a point spread bet, the spread is either added or subtracted from your teams total to come up with an adjusted final score. For example, if you wanted to place a point spread bet on the Dallas Cowboys to win a game against the Chicago Bears, but the point spread was Dallas -3, you would have to subtract 3 points from the Cowboys final score to determine the adjusted final score. Dallas in this case is the favorite and expected to win, so to be fair to bettors of the other team, 3 points are subtracted from them, or 3 points are added to the Bears. Point Spread wagers are usually paid at 11-10, meaning you have to bet $11 to win $10 additional. If you lose, you lose $11. If you win you collect $21, your original $11 plus $10. Point spread bets are normally found on Football and Basketball.
Moneyline bets are a little different. In these bets you are betting on a team to win and if you want to bet on a favorite, you will place a larger bet to win the same amount of money as the person betting on the underdog. An example of this would be if you wanted to bet on the New York Yankees and they were the favorite against the Boston Red Sox. In this case you might see a moneyline of New York -135 and Boston at +125. This means if you want to bet on New York you will have to place a $135 bet to win $100. They are the favorite and should win, so you have to bet more to win $100. A bet on Boston would only have to be $100 and would win $125 if they did win. Moneyline bets can be found in Football and Basketball, but are also the main way to bet on Baseball, Hockey, Boxing and MMA.
You may have noticed that in both the above examples, things aren't exactly even or fair. In point spread bets you bet $11 to win only $10 and in moneyline bets one team is $135 to win $100, while the other you bet $100 but only win $125, not $135. The difference in both cases is called the "vig" or the house advantage. This is how the sports book makes it's money. It's goal is to take in the exact amount of money on each side of a game. When that happens, all the losing bets pay all the winning bets and the house just makes the vig as their profit.
This is why the odds change on games constantly. It's not because new information comes in on the game every hour or two, although that can be a reason for a change in the odds, but because people are placing bets on one side more than the other. When this happens, the sports book makes the odds more enticing to the other side in hopes that they will now place bets to equal the bets already received. A $100,000 bet on a team who's odds are at +140 and the other team -130, might make things go to +120 and -110 to get people to wager on the favorite at $110 to win $100 instead of the earlier $130 to win $100.
So, now you know the basics, now what? Your best bet is to start with just one bet at a reputable sports book. Place the bet, watch the game and get the feel of the process. You'll of course want to do a little studying or review of a game before choosing it. Injuries, weather and location play big factors in games. It's also wise to not wager on your favorite team at first. Betting with your heart and not your brain is an easy way to lose money fast. Once you've placed a few single bet wagers, you can then progress into betting multiple games and into more complex bets like parlays and over/under bets.