It's always a good idea to start with intercepts. To find the y-intercept, plug-in x=0, so y=4(20)=4 is the y-intercept. Mark this point (0,4) on the y-axis.
To find the x-intercept, plug-in y=0, so 4(2x)=0; but there's no solution for x when y=0. However, when x approaches minus infinity, y approaches zero. Therefore the x-axis is an asymptote: the curve gets closer to the x-axis as x becomes more negative.
As x increases positively y increases faster, so, after passing through (0,4) the curve rises steeply. The more precise behaviour of the curve around the origin (0,0) helps to draw the graph. When x=-2 y=4/4=1; when x=-1 y=4/2=2, making the points (-2,1) and (-1,2). When x=1 y=8; when x=2 y=16, making the points (1,8) and (2,16). Sometimes it's helpful to set up a small table of x and y values, using x values between -2 and 2 and calculating the corresponding y values.
The result of all these exercises is the production of a fairly accurate graph of this exponential function.