Leroy, you have not provided us with a point, but I'll pick one to show you how to use your point. Let's use (4,5).
First, we know that slope-intercept form is y = mx + b. With our point, we have x and y, the problem gives us m, so we have to find b.
5 = 3(4) + b
5 = 12 + b
b = -7
Soooo, our equation is y = 3x - 7.
Hope this helps!