Book excerpt: In recent days, people around the world are living in panic when the Covid-19 epidemic is raging in Wuhan city - central China. On January 31, 2020, the World Health Organization (WHO) declared the Covid-19 epidemic to be a global emergency medical condition. This makes everyone's spirits even more confused. Where I live and work, in Vietnam, people flock to buy medical masks. Many businesses have taken advantage of this panic mentality to reap illicit profits, by selling medical masks and hand sanitizers for 10 to 12 times the normal price. Of course, the government has intervened to stabilize the situation, but people's psychology is still insecure. As a doctor, I believe the panic comes from our inadequate knowledge of coronavirus, how it spreads. As well as knowledge about medical masks: "How to use medical masks properly and effectively, to protect yourself and those around you?" So I wrote this booklet, with the desire to give people a simple and useful understanding of coronavirus and how to prevent it from spreading in the community by wearing a proper face mask. Content includes: 1. Basic knowledge of coronavirus, as well as how it is transmitted in the community. What to do if you have signs of someone infected with coronavirus? 2. What types of medical masks are used and work to prevent coronavirus infection in the community? And how to use medical masks properly and effectively to protect yourself. 3. Some important notes to improve the body's resistance, help you fight coronavirus. Sincerely thank you!