A negative test result means that the virus that causes COVID-19 was not found in your sample.  For COVID-19, a negative test result for a sample collected while a person has symptoms usually means that COVID-19 did not cause your recent illness.
However, it is possible for this test to give a negative result that is incorrect (false negative result) in some people who are either infected with SARS-CoV-2 or who have symptoms of COVID-19.  If you do have or develop symptoms of any illness, you should contact your healthcare provider, who will take into account the test results along with your symptoms and your medical history – including possible exposures, and where you have recently traveled – in deciding how to care for you.  It is important that you work with your own primary care healthcare provider to help you understand the next steps that you should take.
A negative test result does not mean that you should stop following the current state, local and CDC guidelines for your area (which may include wearing a mask when in public or social distancing).  It may help you to make decisions about your current health and your potential risk of infecting others.  Most importantly, a negative test result does not mean that you cannot contract COVID-19 in the future.