If you are curious to see what the difference is between online and live poker (and you happen to live in Canada) I would recomend that you check out the Red Hot Poker Tour.
If you are in the US (in a major city), I'm sure there are free live games going on, or you could even join a poker league -
http://www.amateurpokerleague.com/ is a site that I found through Google that you might like to check out.
I'll let the more experienced B&M players handle this thoroughly, but playing live you have the benefit (and drawback) of physical tells, which is a massive difference. Get comfortable playing live for free, and then hit up the casinos/live games. But that's just my 0.02 cents.
Quick note - obviously, you're going to have some crap play at these free events. People usually aren't staking anything on the outcome, so they can play pretty un-realistically. Find a league that has SOMETHING at stake - Red Hot funds a WPT buy-in if you have the most point at the end of the season. Find something like that, so that at least there is SOME motivation to play decent.