Edit Menu: Select
From Audacity Manual
All CTRL + A
Selects all of the audio in all of the tracks.
None CTRL + SHIFT + A
Deselects all of the audio in all of the tracks.
Left at Playback Position [
When Audacity is playing or recording, sets the left boundary of a potential selection by moving the cursor to the current position of the green playback cursor (or red recording cursor). The selection can then be drawn by using "Right at Playback Position" (below).
Right at Playback Position ]
When Audacity is playing or recording, sets the right boundary of the selection, thus drawing the selection from the cursor position to the current position of the green playback cursor (or red recording cursor). This is a quick way to mark a selection for future editing while playing or recording.
Track Start to Cursor SHIFT + J
Selects a region in the selected track(s) from the start of the track to the cursor position (or extends the current selection so that it starts from the start of the track).
Cursor to Track End SHIFT + K
Selects a region in the selected track(s) from the cursor position to the end of the track (or extends the current selection so that it ends at the end of the track).
In All Tracks CTRL + SHIFT + K
Extends the current selection up and/or down into all tracks in the project.
In All Sync-Locked Tracks CTRL + SHIFT + Y
Extends the current selection up and/or down into all sync-locked tracks in the currently selected track group.