Strawberry runners to multiply plants. There are 2 methods to obtain new plants. Strawberry seeds - the small / tiny grain outside each strawberry is one such method. Seeds are tiny and as a general rule of thumb, the smaller a seed, the more delicate to actually grow a plant out of a seed.
Strawberry plants however are more commonly multiplied by use of runners. After each strawberry season, each plants grows several runners. As you see from below photo, a runner grows in an arch away from the plant and after approximately 20cm touches ground again. That is where the runner starts to grow leaves and roots - while continuing its runner growth. Each runner may grow up to approx 1 meter length and have several small plants.