You can find them by Googling for "free fonts." The site where you find them
will offer instructions for download, but generally they will be provided in
a zipped form, and you'll have to unzip them. Once you have copied them to
the Windows Fonts folder (or used File | Install New Font in the Fonts
folder to browse for them and install them), they will be available in Word.
You install fonts in Windows, not in Word. Fonts that are installed in
Windows and that your currently selected printer is capable of printing will
appear in Word's font dropdown box.