We need the graph of the function:

Comparing with the slope-intercept line function:

Where the slope is m and the y-intercept (the point where the line crosses the y-axis) is b.
In this case:

m=4 means that each step the graph advances 4 in y (vertical direction) and 1 in x (horizontal direction)
and b=0 means that the graph crosses the y-axis at y=0 --> the origin
The graph is as follows: