Using Russian Matryoshka Dolls, this collection demonstrates the effect of Aperture
(the camera's pupil diameter) on Depth-of-Field
(the total distance that is in focus).
There are two sets with four shots each taken at f/2.8, f/8, f16 and f/32 respectively.
In the first set, the focus point is on the first doll. In the second set, the focus point is on the fourth doll.
Step through each set and see how the depth-of-field stretches as the f/number rises. (Note: the aperture itself actually becomes smaller as f/number rises.)
As a Rule of Thumb the Depth-of-Field is about 1/3 in front of the focus point, and 2/3 behind the focus point.