We simply replace values for x and get values for y, these pairs of values can be ordered as points and then plotted in the cartesian plane.
For example, when we replace x = 0 in the expression, we obtain y = -4, so one point is (0, -4).
When we replace x = 1, we obtain y = -6, so another point is (1, -6) and so on.
After we have enough points, we "draw" a line connection such points [The points should be determined in order] giving as result the graph of the expression: