This is a linear function. If x=0, y=0; if x=2, y=4, etc. Plot the points given by these coordinate pairs: (0,0), (2,4), ....
The resulting graph is the straight line drawn thru these points. It has a slope of 2 and a y-intercept of 0.
If you meant y = 2^x, then you have an exponential function, which is an entirely different matter.