A cubic function is one in the form f(x) = ax3 + bx2 + cx + d.
The "basic" cubic function, f(x) = x3, is graphed below.
The function of the coefficient a in the general equation is to make the graph "wider" or "skinnier", or to reflect it (if negative):
The constant d in the equation is the y-intercept of the graph.
The effects of b and c on the graph are more complicated. However, if you can factor the right side of the equation, you can find one or more x-intercepts, and use these to sketch the graph. (Some cubics, however, cannot be factored.)
A cubic function may have one, two or three x-intercepts, corresponding to the real roots of the related cubic equation.