Edit Toolbar
From Audacity Manual
Cut or CTRL + X
Removes the selected audio data and places it on the clipboard.
Copy or CTRL + C
Copies the selected audio data to the clipboard without removing it from the project.
Paste or CTRL + V
Either inserts the clipboard contents at the position of the selection cursor, or replaces a selected area with the clipboard contents.
Trim or CTRL + T
Deletes everything but the selection. Does not affect audio outside the selected clips.
Silence or CTRL + L
Replaces the currently selected audio with absolute silence.
Undo and CTRL + Z
Reverts the last editing operation. Audacity supports unlimited "stepwise" undo. This means you can undo every editing operation back to the last time the project was opened, but you can't undo one particular edit without also undoing any changes made after that edit. You can review your editing history and jump straight back to any particular edit point at View > History.
Redo or CTRL + Y (on Mac SHIFT + CTRL + Z)
Restores the previous editing operation that was just undone. Note: If you undo an operation then perform any new one that appears in the Undo History, you can no longer redo that undone operation.
Zoom In or CTRL + 1
Zooms in to a higher magnification level. You can continue to zoom in until you reach the level of displaying individual audio samples.
Zoom Out or CTRL + 3
Zooms out to a lower magnification level. You can zoom out so far as to fit 228 hours of audio on the screen.
Zoom Selection or CTRL + E
Zooms a selection region in or out so that it fits in the available horizontal window area. The button is therefore grayed out unless a selection region is made.
Fit Project or CTRL + F
Zooms in or out so that the entire audio of the project fits in the available horizontal window area.
