The temporal preposition ‘für’ is used when indicating duration (e.g. for a week).
‘Vor’ is used to indicate an event or activity that started and ended at some point in the past (English equivalent of adding “ago” to a time expression; e.g. four weeks ago / vor vier Wochen).
The temporal preposition ‘seit’ is used to indicate something that began in the past and continues into the present, as can be seen in this translation of the third example under “Seit wann?” above:
Ich fahre seit einem Jahr Auto. / I have been driving since last year.
Literally translated, “seit“ in German means since, but it is used other ways, too. In English, “since” is used to mark the beginning of a period of time (I have been here since 2015), whereas in German, “seit” can also be used similar to the way English speakers use “for,” and “vor” is used similar to the way English speakers use “ago.”
Vor 5 Jahren = 5 years ago
Seit 5 Jahren = For 5 years
Seit 2015 = Since 2015