Masks are a simple barrier to help prevent your respiratory droplets from reaching others. Studies show that masks reduce the spray of droplets when worn over the nose and mouth.
You should wear a mask, even if you do not feel sick. This is because several studies have found that people with COVID-19 who never develop symptoms (asymptomatic) and those who are not yet showing symptoms (pre-symptomatic) can still spread the virus to other people. The main function of wearing a mask is to protect those around you, in case you are infected but not showing symptoms.
It is especially important to wear a mask when you are unable to stay at least 6 feet apart from others since COVID-19 spreads mainly among people who are in close contact with one another (within about 6 feet).