Home pregnancy tests detect hCG, which roughly doubles every 48–72 hours in early pregnancy. A faint line means the hormone is present but below the level that produces a strong band, which is typical when you test before or right around a missed period.
An evaporation line is different: it appears after the reading window has passed, is usually grey or colourless, and has no width. Read your test within the time stated in the instructions and discard results read hours later.
The practical next step is to retest with first-morning urine after 48 hours. A genuinely progressing pregnancy usually produces a visibly darker line. A line that stays the same or fades warrants a conversation with a clinician, as it can indicate a very early loss or an issue that needs evaluation.