To start with, you'll open Flash by clicking on the program icon in the directory that you've installed it in. If this is your first time loading the program, it'll ask you to choose either Designer or Developer view, and a resolution that matches your monitor settings (this isn't applicable to versions of Flash prior to MX). For our purposes in this tutorial I've chosen Designer view, and my screen is set to a resolution of 1024x768. (You can always change this later by clicking the "Window" option in the top toolbar and then selecting "Panel Sets".) Once you've finished that, you'll see a blank canvas surrounded by tool sets, like the window above.

