I know this isn't exactly the proper place for breaking news, but I figure the more people know, the better.
TL;DR: WHO declared the virus a global health emergency because they're concerned it might spread to countries that are not prepared to deal with it.
Global health emergencies are declared when diseases have the potential to spread locally once they've arrived to a new country and can result in economic disruption. This doesn't mean it's the Black Plague or Spanish Flu all over again, it just means the virus could become a big issue worldwide if people aren't careful.
Human-to-human contact is possible, but infected surfaces can remain infectious for some time. In terms of transmission it's quite similar to the flu, so do the usual stuff you do for the flu (cover your face with your arm or a tissue when you sneeze or cough, wash your hands thoroughly, and so on).
Symptoms are similar to the flu, but worse, and can develop into pneumonia and severe respiratory issues, including respiratory failure.