Research suggests that transmission mainly happens indoors where people are close together. Face coverings placed over the nose and mouth reduces the spread of coronavirus droplets caused by coughs, sneezes and speaking. The main goal is to protect others. If everyone is wearing one, the risks reduce for everyone.
There is some proof they put out protection to wearers, but are not an alternative for social distancing and hand-washing. Masks can also assist lessen virus spread from infectious people with no symptoms.