In a typical scripted movie, we have to track and manipulate everything from frame numbers to a user's password to the velocity of a photon torpedo fired from a spaceship. In order to manage and retrieve all that information, we need to store it in variables, the primary information-storage containers of ActionScript.
A variable is like a bank account that, instead of holding money, holds information (data). Creating a new variable is like setting up a new account; we establish a place to store something we'll need in the future. And, just as every bank account has an account number, every variable has a name associated with it that is used to access the data in the variable.
Once a variable is created, we can put new data into it as often as we want—much like depositing money into an account. Or, we can find out what's in a variable by using the variable's name—much like checking an account's balance. If we no longer need our variable, we can "close the account" by deleting the variable.
The key feature to note is that variables let us refer to data that either changes or is calculated when a movie plays. Just as a bank account's number remains the same even though the account balance varies, a variable's name remains fixed even though the data it contains may change. Using that fixed reference to access changing content, we can perform complex calculations, keep track of cards in a card game, save guest book entries, or send the playhead to different locations based on changing conditions.
Is that a gleam of excitement I see in your eye? Good, I thought I might have lost you with all that talk about banks. Let's start our exploration of variables by seeing how to create them.