Here are the steps to export the Audio Mixdown:

1. Select the pencil tool from the toolbar.
2. Click once in the ruler above your tracks. A white triangle should appear. Click and drag the left half of the triangle to the beginning of what you want to export. Click and drag the right half of the triangle to the end of what you want to export. This sets the left and right margins. Your project should now be highlighted in blue.
3. Go to the "File" menu > "Export" > "Audio Mixdown..."
4. Choose a location to save you file ("Look in:") and give it a name.
5. If you want to burn your file to an audio CD, you must select Coding as PCM / Uncompressed Waves, Channels as Stereo Interleaved, Resolution as 16 Bit, and Sample Rate as 44.100 kHz
6. Press "Save." Your file will be saved to the location you selected.