The Power Editor has two modes. In cursor mode the arrow keys move a cursor between cells and typing replaces what is in one. In edit mode you are inside a cell and the keys go to the text. Almost everything below is about moving between the two without thinking about it.
Mod means Command on a Mac and Ctrl everywhere else. Pressing ? anywhere in the app opens the same table in a dialog.
Navigation, in cursor mode
Move cursor between cells
Up / Down / Left / Right
Move forward / back (skip merged)
Tab / Shift+Tab
Move down / up in same column
Enter / Shift+Enter
Enter edit mode on the current cell
F2
Replace cell content (any printable key)
A-Z 0-9
Open the Notes cell appending
any letter
Editing
Commit and move to next cell
Tab / Enter
Commit and stay on the cell
F2
Revert and stay on the cell
Esc
Two-step Esc: pressing Esc once reverts the edit you are in the middle of. Pressing it again clears the selection and leaves cursor mode. So Esc never does both at once, and never loses a selection you meant to keep.
Selection and range
Extend selection by one cell
Shift+Up / Shift+Down / Shift+Left / Shift+Right
Extend selection by mouse
click-drag
Clear all values in selection
Del / Backspace
Copy selection (TSV, paste in Excel)
Mod+C
Paste TSV (Excel-compatible)
Mod+V
Fill the cursor's column down
Mod+D
Rows
Move selected row up / down
Alt+Up / Alt+Down
Click row label to select; click cell to edit
mouse
The plan
Save the plan to its file
Mod+S
Undo
Mod+Z
Redo
Mod+Shift+Z
Save is ignored while you are typing in a field, so it cannot fire in the middle of an edit and write half of one.
Help
Open this shortcuts dialog
?
Close this dialog
Esc
Ballooning
Inside the new-plan wizard's ballooning step, the number keys choose what the next balloon will be.