Once a track is created on a draft product, click the Upload Asset box on the right side of a given track on the Create Product track list. Choose a valid audio file and click Open.
The audio will be validated for sample rate, bit depth, codec and file type. If validation is passed, the original file name of the asset and the asset's duration will display in the asset box on the track. If validation fails, click the red asset box for information on why it failed.
See the article on Audio Validation Rules for detailed information on accepted audio formats.