When you look at you calculator, there are all sorts of option.
Make sure you check your book for instructions on the keys you need to be able to use right now. the keys can differ for different brands of calculators. I will give instructions how to use a casio:
If you press the number of the numerator from you fraction
then press the ab/c key (made yellow in the picture) then press the number of the denominator. This way you get the fraction on you calculator. Put it between brackets if you want to use the fraction in a calculation
The key right underneath the yellow key there is a minus sign in brackets. This minus is used when you are calculation with negative numbers.