What is it?
Records a sound in the active sound document and optionally overdubs.

How to use it
When the record button is pressed, the recording process is automatically Paused.  Press the Pause button to start recording.  Select one track to record in mono and two tracks to record in stereo.  The selected portion of a sound will be deleted and the new sound will be inserted.

If the option key is held down, it will play the unselected tracks while recording (overdub).  After recording, you will need to offset the recorded tracks to the left to put them in sync with the other tracks.  Use the Track Offset Tool or delete the unwanted area.  You will probably need to use headphones so the sound your listening to doesn't get recorded too.  Pausing is not allowed when overdubbing.

While recording sounds, the Track Pan area of the Mixer shows the amount of time available for recording in minutes, seconds, and milliseconds or frames depending on the Preference settings. 

Notes
If you are getting warnings when trying to record, it's because the sound document's sample rate or size is not supported by the input device.  Make sure the "Sound In" Preferences are set correctly.  You can also Resample to the correct sample rate and size.

If you would like to increase recording time, give it more memory in the Finder with "Get Info".

Recording will not work if your Mac does not have asynchronous sound input capabilities (able to record while other things are going on).  Some of the older or low cost Mac's may not have asynchronous sound input capabilities.

See "Sound In" Preferences for more information.