Flash Builder does not always import projects folders you have placed in your workspace folder. You have to manually import them using Flash Builder by selecting File > Import... then expanding the General folder and selecting Existing Projects Into Workspace (see image). Click the Next button and use the dialog to select the root directory ( your workspace folder ) and import the projects you want. All the ones you select will now show up in the Package Explorer view.
Liz - are you working with the Day 1 zip file? There is a readme file in that zip that walks you through the setup. The video titled "Using Flash Builder" also walks you through the steps of the setup and the third section of exercise 1 (http://www.adobe.com/devnet/flex/videotraining/exercises/ex1_01.html#a rticlecontentAdobe_numberedheader_1) walks you through the setup as well. The second section of that exercise walks you through the steps of using the project zip files that are on each individual exercise page. HTHs.