Undo

This will undo the last editing operation you performed to your project. Audacity currently supports full unlimited undo - meaning you can undo every editing operation back to when you opened the window.

Redo

This will redo any editing operations that were just undone. After you perform a new editing operation, you can no longer redo the operations that were undone.

Cut

Removes the selected audio data and places it on the clipboard. Only one "thing" can be on the clipboard at a time, but it may contain multiple tracks.

Copy

Copies the selected audio data to the clipboard without removing it from the project.

Paste

Inserts whatever is on the clipboard at the position of the selection cursor in the project, replacing whatever audio data is currently selected, if any.

Trim

Deletes everything but the selection.

Delete

Removes the audio data that is currently selected without copying it to the clipboard.

Silence

Erases the audio data currently selected, replacing it with silence instead of removing it completely.

Split

Moves the selected region into its own track or tracks, replacing the affected portion of the original track with silence. See the figure below:

Duplicate

Makes a copy of all or part of a track or set of tracks into new tracks. See the figure below:

Split at Labels

Uses the split function to give you seperate tracks for every label. The source track remains unchanged.

Select the label track(click on the track panel), then select the track you wish to split by SHIFT+click'ing on its track panel. Now activate the Split by Labels function.

The result is that for each label, a new track will be created that contains a duplicate of the material up to the next label or the end of the track, whichever comes first.

Select All

Selects all of the audio in all of the tracks.

Select Start to Cursor

Selects all the audio from the start of the timeline to the current cursor.

Select Cursor to End

Selects all the audio from the cursor to the end of project, which is as far as audio exists in the project.