The main transmission for the Corona virus is airborne. The touching of surfaces then your face transmission is secondary transmission...
That means most people catching it, get it from breathing it in.... it can stay airborne for up to a high of 14 minutes according to the tests they've done in the laboratory with particles the same micron size as this virus...before they fall to surfaces.
Masks keep you from exhaling heavier viral loads in to the air, but do not stop the virus altogether....from entering the air....it just reduces it drastically.... which reduces the chances of you breathing it in. Masks also reduce the droplets that fall on surfaces when coughing and sneezing, which in turn, also reduces spread.
The necessity for masks, is because we have found out many people have caught it, And have it with no symptoms at all, and people who do get sick are infectious and spreading it before they develop symptoms of sickness.
We can't just say, like with the flu, to stay home when running a fever with your cough....That is the infectious period.
This corona virus sucker, is sneaky! Thus, masks being a relevant preventative measure to reduce the rapid spread of the virus, where 1 person is spreading it to 2 or 3 people, we can work to cut it down to every 1 person, spreading it down to 1 other person. That's called an "R naught" factor.
If we can get it to below 1 person passing the contagion to 1 other person, but say to 0.7 people, then we have killed the virus, it will die....poof, gone!
Though possible, it's unlikely we can get it that low, but getting it to an R1, a 1 to 1 infection rate, then less people will die, than now.
Going back to masks, if you are wearing one, and are not sick, it isn't stopping you from spreading it, well....cuz you are not sick.... but the mask likely keeps you from breathing in a heavier viral load of the virus in a room with someone infected.... the less viral load, the less sick you get, when you catch it, is what I heard docs on tv discussing.....
This is also why being outside is safer than indoors... outdoors dispersed the airborne particulars in to lighter load.