How do I insert a variable in MXML (Flash builder 4)?

Answer 1

If this another value suppose to be "aries", than you've been doing it wrong. You've defined new myVar variable where you should've only change its value.

This line defines new variable for the current scope:

var myVar:String = "aries";

This line changes the value of an existing variable:

myVar = "aries";

Answer 2

Not entirely sure what your question is, but are you trying to change a label in the UI based on the button click? If so, you'll want to add [Bindable] above your declaration of myVar.