Rather than solve the entire problem for you, I'll give you some hints to help you get started:
1. The amplitude of your sinusoidal graph is |3|, or just 3.
2. Because of that, your graph begins at the point (0,3).
3. Because this is the cosine function, your graph descends from (0,3) to y=3 and then begins to ascend (back to y=3).
4. The coefficient of x is "one half pi," or pi/2. Call this "b".
5. The period of your function is 2pi/b. Here, b=pi/2.
Dividing, [2pi]/[pi/2] = 4.
6. Mark your horizontal axis as follows: x=0, 4, 8, 12, 16, ...
7 Draw one cycle of the cosine function with amplitude 3. It must begin at (0,3) and end at (4,3) (which covers one period).
8. Draw another cycle or two, beginning at (4,3) and ending at (8,3), and so on.
