Typing some simple fractions automatically in Word and Outlook
As part of Word’s Autocorrect settings, some simple fractions will show as a symbol when you. For example, if you type in 1/4 and then space straight afterwards it’ll show as ¼.
It’s done automatically from File | Options | Proofing | AutoCorrect Options | AutoFormat as you type | Fractions (1/2) with fraction character (½).

It’s on by default but you can turn it off.
Only three fractions
The AutoFormat as you type, Fractions option only works for THREE fractions half, quarter and three-quarters.
Only ½ ¼ ¾ are setup.
Not even some other common fractions like 1/3 and 2/3 are included.
For other fractions, you have to use either Insert | Symbol or some other trickery like AutoCorrect to make fractions.
See Typing common fractions in Word and Outlook
Make your own fractions in Word and Outlook
More fraction options with Equation Editor in Word.