If the control line does not appear, your test should be discarded, as it's likely not going to give you an accurate result.

When you take a home pregnancy test, you look at the results window to see whether there are two lines or just one. The first line is the control line ... of the test ("not pregnant") is typically ...

an evaporation line, which is a faint streak may appear on a pregnancy test. This does not mean you're pregnant. This line should be colorless, which is how you can tell the difference.