Strawberries produce an above-ground branch (shoot) with very tiny leaves. These almost-leafless branches are called stolons. These develop a tiny plantlet, the crown at the tip (apical bud). This crown grows and weighs down the end of the stolon. As the crown bends the stolon toward the earth, it accumulates auxin (because of the horizontal position) and roots begin to develop. When it touches down on the ground, the roots penetrate and root the crown into the soil.
Since each plant may make a dozen of these crowns, you do not need to buy a huge number of strawberry plants to make a good strawberry patch. Within a year or so you can have a vast number of plants to move around in your patch.