After you start Flash, setup (2) layers, "actions" <-(lock it) and "component".

layer setup


Next, hit Ctrl+F7 or go to Window->Components to pull up the Component Panel. Then, drag (3) TextInput components to the stage. You can resize them, give the group a name and name each instance. I just resized them to widths of 60 and gave them instance names of s1, s2 and s3.

grab components

Once that's done, select your actions layer and pull up the actions panel and let's start some coding!