Fantastic! You saw that the position of the object in the beginning was at $$0$$, it went up to $$20$$ and then returned to $$0$$.
Look at the animation alongside to understand how to interpret the graph. The figure initially moves to the right, stops once it reaches a maximum displacement of $$20 \, \mathrm{m}$$ and then turns around and walks back. As it walks back, the displacement keeps decreasing, until it reaches a value of $$0$$, when the figure returns to the original position.

Such graphs are called position-time graphs because they plot the position of an object as a function of time.