This means that you were infected with hepatitis C at some point but your body was able to clear (get rid of) the infection, and so you no longer have the virus. Unfortunately, if you are exposed to hepatitis C in the future, you can be re-infected.
Some people never clear hepatitis C and so the virus is still detectable in their blood. This means they are at risk for the complications of having hepatitis C, for instance iver damage, and that they can transmit it to others. Luckily there are well tolerated medications that can treat hepatitis C in as little as 8-12 weeks.