The primary way you can get head lice is when your head comes in direct contact with the head of an infested individual. Head-to-head contact like that doesn't guarantee that the infestation will spread, but it gives lice the best opportunity to move from the hair of the infested person to your hair.
Head lice don't jump, swim or fly. Without strands of hair to grab with the claws on their legs, they have trouble getting around at all. However, they can crawl pretty quickly along the hair, so if your hair comes in contact with an infested head, it doesn't take much for a louse to hitch a ride on a strand of your hair and make its way to your scalp.
If a female louse makes it onto your head, she will start laying lice eggs (about four a day). Those eggs will hatch, the lice will become adults, and females will continue to lay eggs. This means that unless you kill the lice and eggs, you will continue to be infested.
Head lice prefer to stay in their protected environment close to the scalp (where they feed on human blood). However, it isn't uncommon for them to get knocked off the head and onto a pillow, brush or hat. If your head comes in contact with one of those items, it is possible a healthy louse could latch onto your hair and make your head its home.
If you are asking yourself, "How can I get lice?" it suggests you may be worried that you or a family member has been exposed to others with head lice. If so, follow-up questions might be: Do I have lice? What are the symptoms of lice? How can I kill lice? Which lice treatment is best?