Fractions can be written in two ways: with a diagonal fraction bar or a horizontal one. Diagonal fraction bars work best in tight places, such as in a text paragraph or when in a larger fraction.
$a/b$
becomes
The horizontal bar is clearer when you have more room, such as in a
formula paragraph. The command is a little more complicated, because
the numerator and denominator are often complicated themselves. A
horizontal bar fraction is written as
\frac{numerator}{denominator}.
$$
\frac{a/b-c/d}{e/f-g/h}
$$
becomes
Practice:
Construct a couple of nested fractions yourself.