How do I know if I have COVID-19?

WHO has produced definitions for suspected and probable cases of COVID-19 which you can view hereand I've summarised them below

Covid-19 is a disease caused by a novel coronavirus, SARS-CoV-2

suspected case: 

    A:   acute respiratory illness: fever + cough or shortness of breath and return from high risk country within the last 14 days
    B:  acute respiratory illness: fever + cough or shortness of breath and contact with person with confirmed COVID-19 within the last 14 days
    C:  patient with unexplained severe acute respiratory illness in hospital.

probable case: 

    A:  unexplained severe acute respiratory illness and inconclusive test results
    B:  unexplained severe acute respiratory illness and gtesting not available

Confirmed case:

     blood tests detect the virus or antibody to the virus; virus may be detected before symptoms, antibodies are detected five days after the onset of symptoms.

Since carriers of the virus may have no symptoms, this implies the numbers of people transmitting the disease is much larger than the confirmed cases published daily.