A positive RT-PCR nasal swab means the virus was detected. It does not tell us if you are infectious or not. A negative test means the virus was not detected on the nasal sample. You could still be infectious with a negative result.
A positive IgG serology (antibody) test means an antibody was detected. Antibodies may appear days to weeks after an infection, but may not appear for 3 weeks or may never appear. A positive antibody test is difficult to interpret with our current understanding of the disease. It may represent recent infection, remote infection, or possibly a false positive. We cannot say anything about immunity at this time. A positive IgG does not mean you are immune. Antibody tests should not be used as the sole test to determine if someone has the disease.