How would you graph -5/4 on a number line?

A number line extends from $- \infty$ on the extreme left to $\infty$ on the extreme right. Zero will be in the center. Just one unit to the right of zero is $1$ and $- 1$ one unit too the left of zero.
$- \frac{5}{4} = - 1 \frac{1}{4}$, hence it lies between $- 2$ and $- 1$. $- 2$ will be one unit further to the left of $- 1$ by one unit.
If we divide the distance between $- 2$ and $- 1$ in to four equal parts, $- 1 \frac{1}{4}$ will be the one just left of $- 1$ (or three fourths to the right of $- 2$).