This isn't as difficult as it sounds. First, we need to find the slope so we do 
 
(y(2)-y(1))/(x(2)-x(1)) and plug in using the points we have: 
 
(-3-3)/(2-0) = -6/2 = -3 
 
Now we use the point slope formula which is y – y1 = m(x – x1) 
 
From this, we again plug in using one point and the slope we have. Let's choose (0,3) because it's simpler. 
 
We get: y-3 = -3 (x-0) 
y - 3 = -3x 
y = -3x + 3 
 
I hope this helps. :)