While the mechanics of the game are the same, there are vast differences between casino and Online Poker. Those differences change how you play. If you don't understand then you should not play in both.
The first difference is obvious. When you play in a casino you are able to see your opponents. That gives you the opportunity to study their play and watch for indications of the strength of their hands. This is known as picking up on ‘tells', a valuable way to increase profits. Online you can't see your opponents and have to rely on betting patterns. In both, betting patterns are more valuable than physical tells, especially when playing with good players. In face to face play a tricky opponent can set you up by exhibiting a tell when holding a weak hand. You catch him at it and assume that tell means he has a weak hand. Later he will exhibit the same tell, but when you call, expecting he is weak, he shows you a monster hand. This is called a reverse tell.
Online poker runs at a far faster pace. In a casino, a fast game may have 40 hands an hour. Online you will be playing far more hands an hour, perhaps double the rate as in a casino. In a casino, you can play at only one table. Online sites allow you to play as many as four to six tables at the same time. A good player can maximize his hourly win rate by playing more than one game at a time.
The rake, how much the house takes from the pot to pay for hosting the game, is lower online than in casinos. Casinos have to pay dealers, floor men, cocktail waitresses, as well as for tables, chips and cards. Online a server can host many games at the same time, making online overhead much lower. Most online sites charge a 5 percent rake, with a two or three-dollar maximum. Casinos usually charge 10 percent with a maximum of up to five dollars. In addition in live games the winner is expected to toke (Tip) the dealer. Say you win a one hundred-dollar pot. Online the site takes three dollars. In a casino the rake could be five dollars and the toke a dollar. Your online profit is 97-dollars, while in the casino it is 94-dollars. That three-dollar difference adds up over the many hands you play. In a hundred wins the difference is 300-dollars. That's not chump change.
Online you can use a "chat box" to communicate with your opponents, but this is cumbersome and limited to short messages such as "Good hand"in the casino you can chat up a storm, socializing with the other players. This gives you an opportunity to use conversation to affect how you opponents play
To play in a casino, you have to dress up and drive to the casino. If you smoke, most casinos have no smoking card rooms. If you are having a nicotine fit, you have to leave the game for a while to go to a place where smoking is allowed. You can play or you can smoke, but you can't do both at the same time. On line you can sit in your easy chair naked, chain smoking and no one will know or care. You also don't have to dress and drive to the casino. Online play is much more convenient.
Both card rooms and the Internet have their advantages and disadvantages. If you live near a casino you can go out to play when you feel like playing with humans, you can socialize with. You can play online if you have only a limited time to play, or just want to avoid the inconvenience associated with a casino. If you don't live within driving distance and want to play, you have only one option, the net.