A fraction simply tells us how many parts of a whole there are. You can recognize a fraction by the horizontal line that is written between the two numbers: one number above and one below the horizontal line.
To express a fraction in American Sign Language (ASL), the handshape of a number is transformed into another number as it moves downward. Eg. 1 -> 2 for 1/2 or 3 -> 4 for 3/4 from the upper space to lower space across the imaginary horizontal line from the signer's perspective.
The palm orientation generally faces in between number one and nine in fractions. For the rest of numbers beyond ten, the rules of palm orientation are the same as cardinal numbers.
half, one-half, 1/2
You get the idea.
Christopher Kurz in the YouTube video above demostrates how to explain math concepts in ASL, specifically proper fraction, improper fraction, and mixed fraction.