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 the last time the document was saved.

Redo

This will redo any editing operations that were just undone. After you perform a new editing operation, including simply resizing a track, 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.

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.

Insert Silence...

Prompts for a dialog indicating the number of seconds of silence to insert, then inserts that amount of silence at the current selection cursor position in the project, replacing whatever audio data is currently selected, if any.

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:

Select All

Selects all of the audio in all of the tracks.