How to go from $5\pi/4$ to $\pi + \pi/4$? 
Use standard triangles to find exact value of $\cos(5\pi/4)$.

Example states that $5\pi/4$ is equal to $\pi + \pi/4$ but doesn't list the steps to get $\pi + \pi/4$...

$\pi$ is just like any other number. So you can do $\frac{5 \pi}{4} = \frac{4 \pi}{4} + \frac{\pi}{4} = \pi + \frac{\pi}{4}$ just like you can do $\frac{5}{4} = \frac{4}{4} + \frac{1}{4} = 1 + \frac{1}{4}$.
