the best way to graph this is to put in a value for y and find out what the x value or values come out to be. Let's start with y=0
Plug 0 in where you see y
3*0^2=x
0=x
so our first point is y=0, x=0 or (0,0)
Let;s say y=1
Plug 1 in where you see y
3*1^2=x
3*1=x
3=x
so our next point would be y=1, x=3 or (1,3)
Let's say y=-1
Plug in -1 where you see y
3*-1^2=x
3*-1^2=x
3=x
So our next point would be y=-1 , x=3 or (-1,3)
Put the points together and you get a parabola which opens to the right. It looks like this: