how to tell the difference between a evap line and faint line

Elizabeth

ok so can someone please explain how to tell the difference between a faint line and a evap line on a cheap dollar store pregnancy test I used one about a week ago and I thought it was negative but I looked at it today and it had a very light faint line I'm so confused but does this mean I could be pregnant? I have not retested yet but plan to tomorrow any info is greatly appreciated