Windows shortcut
F4
Mac shortcut
⌘T
While editing a formula, this shortcut toggles cell references from relative to absolute, to partially absolute, back to relative again:
A1 $A$1 A$1– > $A1– > A1
It’s much faster and easier than typing $ characters manually.
To convert an existing formula, enter cell edit mode, place the cursor in or next to the reference you’d like to convert, then use the shortcut.