Wearing a mask will help stop the spread of Covid-19.
Wearing may help you from getting the virus.

Masks can be worn to protect the wearer from getting infected or masks can be worn to protect others from being infected by the wearer. 

Protecting the wearer is a little more difficult: It requires medical-grade respirator masks, a proper fit, and careful putting on and taking off.  I think even a simple mask will help keep you a little safer and keep you from sucking in bad air.
Also a mask reminds you not to touch your face. 

Wearing masks help to prevent transmission to others and this is their most important use. 

Keeping our friends and family from getting sick by wearing a mask is the most important thing we can do.
If we can lower the likelihood of one person infecting another, the impact is huge.

Wearing a mask will help stop the spread.
This means a mask will help stopping the spread to your girlfriend, wife, parents, best friend and your surfing buddy.
If we can stop the spread even a little while they are working on treatments and vaccines. 
Then we have a shot at surviving this pandemic.

Even a small reduction in spreading this virus will result in a huge decrease in deaths.

Luckily, blocking the transmission of the virus at the source, your mouth and nose, is easy.
It's as easy as wearing a mask.

And it can be accomplished with something as simple as a cloth mask made out of an old tee shirt or bandana.

Wash your hands and stay safe.