When typing in the calculator, use /
So let's say I wanted to put 3 over 4, I would put 3/4
If you mean when asking a question, go onto LaTeX, which is beside Image, and click on it
Then to put in a fraction, you would type \frac then put in your numbers like this {}
Ex. \frac{3}{4}
This is what it looks like: \(\frac{3}{4}\)