Having a purposefully suppressed immune system (long story), I have worn mask and gloves for nearing 5 years. It is natural for me to avoid anyone coughing and sneezing, as that is how droplets containing a virus are broadcast. I spent 6-7 months last year down with various viruses.
Even if you do not have active virus - or symptoms - you may still carry the virus and broadcast it by coughing or sneezing. We are talking about a virus that is about 1/10 the size of a bacterium. Much tinier than any human cell. Best observed via electron microscope.
The normal vector is our hands. Set aside wearing a mask for the moment. Everything we touch in the public physical world has been touched by others. Many viruses have probably been deposited there, and viruses are not technically living things (argument there) - so they remain forever. We touch and pickup the virus - think wet paint.
Our eyes itch so we transfer the paint (virus) from hand to eye when we scratch the itch. Thus, we infect ourselves. There are millions of viruses in existence, but only 3,000 or so have been scientifically identified and described. All of the others are simply unknown and their effects on mankind are unknown.
There are many corona viruses, this being simply a novel mutation of that category of virus. It was discovered in 2019, thus its name. About 20 vaccines are in development but will probably not be available until 2021. 80% of those with the virus show only mild symptoms, thus may go about spreading the virus without knowing it.
So, masks are good, but gloves and multi-times daily hand washing (after touching anything in public) is better. I have been paying attention to this, as in addition to my suppressed immune system, I have a recent tendency to develop pneumonia. Covid19 is a respiratory virus and so I am acutely at risk.
There is a British doctor (PhD/Nursing instructor) on YouTube who updates daily and is a wealth of information regarding the science of and practical means of avoiding the virus. Here is an excellent vid on self-isolating and about avoiding the virus in the first place.