Let's re-arrange the equation a little to look like this:

From the term, we can tell 2 things. The squared tells you that it is a parabola. The negative sign tells you that it opens downward.

Next, the easiest thing to do is find the y-intercept. Let X = 0 and you'll get the point that the graph intersects the y-axis.

Since this is in the high school help forum, I would assume you know the quadratic formula, so use that to solve for the x-intercepts.

Then you can simply connect the 3 points with a smooth curve (where your y-intercept is your maximum point) and you'll have your curve.