HPT help, please and thank you.

AF isn't due until December 4th.. But I got really antsy and took a test with FMU. I waited 3min (like the intstructions said) and no second line had popped up... I assumed BFN and went to start breakfast. About 10min later I came back to throw the test away. Now there is the faintest line.. Not sure when it appeared.. And something had to make that line happen! I know I'm early on testing so I will test again December 5th (if no AF) but what are your thoughts? Not a lot of pregnancy test experience. Also, I know evap lines exist.. But what exactly are they? What does it mean?