Word keyboard shortcuts on a Mac
Most Word shortcuts carry straight over from Windows with Command in place of Control. The ones that catch people out are the function keys, Paste Special, and the document-navigation keys, because Mac keyboards don't have the same physical keys.
The rule that covers most of them
Take any Windows Word shortcut and swap Ctrl for ⌘ Command. That gets you the large majority of them working on the first try.
Where Windows uses Alt, the Mac uses ⌥ Option. Shift stays Shift.
Everyday formatting
Action Shortcut Bold ⌘ B Italic ⌘ I Underline ⌘ U Double underline ⌘ ⇧ D Font dialog ⌘ D Grow font one point ⌘ ] Shrink font one point ⌘ [ Superscript ⌘ ⇧ = Subscript ⌘ = Copy formatting ⌘ ⇧ C Paste formatting ⌘ ⇧ V Paragraphs and styles
Action Shortcut Align left ⌘ L Center ⌘ E Align right ⌘ R Justify ⌘ J Single line spacing ⌘ 1 1.5 line spacing ⌘ 5 Double line spacing ⌘ 2 Heading 1 / 2 / 3 ⌘ ⌥ 1 / 2 / 3 Normal style ⌘ ⇧ N Insert hyperlink ⌘ K The ones that differ from Windows
These are worth learning deliberately, because muscle memory from Windows fails here.
Action Windows Mac Paste Special Ctrl Alt V ⌘ ⌃ V New comment Ctrl Alt M ⌘ ⌥ M Track changes on/off Ctrl Shift E ⌘ ⇧ E Start of document Ctrl Home ⌘ ↑ End of document Ctrl End ⌘ ↓ Note ⌃ Control in Paste Special — that's the Control key, not Command. It's one of the few places Word for Mac still uses it.
Make the function keys work
Shortcuts like F7 for spelling do exist on the Mac, but by default the top row controls brightness and volume instead.
Either hold Fn with the F-key, or turn the behaviour around permanently: System Settings → Keyboard → Keyboard Shortcuts → Function Keys → Use F1, F2, etc. keys as standard function keys.
On a Touch Bar Mac, hold Fn to make the function row appear.
Find or change any shortcut yourself
Word ships with a full editable map, which beats hunting through lists.
Go to Tools → Customize Keyboard. Pick a category and command to see its current shortcut, or click into Press new keyboard shortcut to assign your own.
If you want a Windows shortcut that doesn't exist on Mac, this is where you add it. Word warns you if the combination is already taken.