In the Equation it asks for 3 things; pi (3.14), r (The radius), and h (the height).
In the question, it says that the radius is 1 foot and that the height is 4 feet. From there all you need to do is insert those numbers where it's shown in the equation. This makes the equation go from this:
To this:
From there you follow PEMDAS/GEMDAS. And should have your answer.