The default way of inserting a footnote in Word is to open a dialogue that lets you choose some options, then press Enter to add a footnote and begin writing.

You can skip this dialogue and use a keyboard shortcut to enter a footnote number immediately, by going to Word Options > “Customize Ribbon” > “Customize” Keyboard Shortcuts.

At the next dialogue (Customize Keyboard) select “All Commands” at the “Categories” pane and scroll the right pane (“Commands”) until you find the “InsertFootnoteNow” command.

Select and assign to this command any keyboard shortcut you find convenient (I use Ctrl+Alt+F). Next time you need to insert a footnote, press this shortcut and start immediately typing your text to your new footnote. Enjoy!