There are many differences between the two versions of poker. First of all, if you plan on playing no-limit hold’em in a live casino, the games are going to be much softer. People tend to play more loosely and passively in a live setting, often because they have traveled far to play and folding every hand just isn’t as fun. Also, since unlike playing online, they don’t have the option to play multiple tables at once. This naturally makes the games play looser.
Online, since the action moves much faster, players are more inclined to play tight. Since it won’t take one to minutes to get more cards, only the loosest players at the table will be playing a hand like 64o under the gun. Secondly, online players tend to be much more aggressive, at all stakes. It is not uncommon to see an online pro-3-bet a hand like QJs, but seeing 3-bets that aren’t premium in a live setting is rare, except at perhaps the $5/$10 level and above. Open limping tends to be unusual and continuation bets with nothing are the norm. Lastly, if you play online and choose not to bet on the flop, you should expect that another player will try to take the pot away from you.