You are either born with them, or you have a skin condition but having a few extra freckles appear around the age of puberty is perfectly normal. If you notice a freckle or a mole anywhere on your body that seems suspicious to you, contact a doctor immediately.
Well, you get freckles by the sun. Freckles are also known as "Sun Kisses" As Katy Perry once said. Freckles are a type of sun damage. If you have a more pale complexion, you are more likely to get freckles.