Viruses are not alive. Their only reason for existing is to reproduce and spread to as many hosts as possible.
This is a new (novel) type of coronavirus. Humans have no immunity. Every human can be infected. We do not yet know if any of us has “natural” immunity (cannot get infected).
The virus kills a relatively low percentage of people (estimated 0.6% to 1%), compared with Ebola at 50%. With Covid, more people are left alive to infect. It is easily transmitted through the air (respiratory), much more efficient than requiring close physical contact (Ebola), and mostly kills old people, especially over 80. More younger humans are left alive to infect.
About 50% (estimate has varied over time) of people infected with the virus have no symptoms (asymptomatic) and can spread the virus. This is unusual for a virus and greatly increases its ability to expand into many humans. (Note: the percent has changed over time.)
Emerging research suggests that people may actually be most contagious during the 48 hours before they start to experience symptoms. It can take between 1-14 days for COVID symptoms to show up. More time for infected people to spread the virus and infect others.
It “waits” for humans to help it expand by leaving their homes, not using face masks or doing physical distancing, crowding inside rooms with lots of unmasked people and poor ventilation, not washing hands, etc.
If you are infected no one knows if you will be immune or for how long. Some viruses, such as in the seasonal flu, regularly mutate, so humans have relativity short immunity time.
On the plus side, it is a “starter” virus, much less deadly than SARS, with a 10% death rate or Ebola at 40%. It is less contagious than measles, which has very tiny droplets, that can remain suspended in the air for up to two hours after someone with measles has left an area.
Also a plus, COVID has not mutated much in the past 6-7 months, making vaccines easier to work for longer periods of time (assuming this will continue). Flu viruses mutate every year with new vaccines required.