The abbreviation i.e. stands for the Latin "id est," which means "that is." It's mainly used in academic writing, although people who don't mind sounding a little pompous may use it in casual writing or even in speech.
You can usually avoid using i.e. by using instead the phrase "that is" or "in other words." But whichever you use, don't forget to put periods after each letter and a comma before and after: "Here you are with your picture flashed on the big screen at America's busiest intersection, i.e., Broadway and 42nd Street!"