If you have a point x-coordinate must be zero, so to find P you need to substitute x=0 into the equation. This then gives P=(0,y), where y is to be found.
To find the minimum point you need to complete the square. Say you have
y=(x+a)2+b. Then since any square number is always greater than or equal to zero, we have
y≥b, and it is only
equal to b when
(x+a)2=0, which happens when
x=−a, and so the minimum point must be at (-a,b). See if you can apply this to your problem.
When you plot the graph, you need to plot the minimum point (which is where the curve 'bends' back upwards), and the point where it crosses the y-axis. If you're feeling keen you can also find where it crosses the x-axis (i.e. the roots of the polynomial), and then you have more than enough information to make a convincing sketch.