Recall that $$v = \frac{dr}{dt} \implies r = \int v(t) dt$$. So, the displacement of an object is the integral of velocity. Whenever you see an integral, think of area under the curve. If the curve is below the y-axis, the area is negative.
For example, the area in the first rectangle in the animation equals the displacement from $$t=0$$ to $$t=1$$. The area of the second rectangle equals the displacement from $$t=1$$ to $$t=3$$.