Learn Hardcore Russian: Откуда ты привёз сувениры?

Откуда means from where. It asks about the origin point of an action or object. It cannot be replaced by Где, which only asks where (location) without specifying movement from that place.

Why is the verb привёз used here and what does it imply about the time and completeness of the action?

Привёз is the past tense of the perfective verb привезти (to bring). Using the perfective past:

Places the action in the past.
Emphasizes that the bringing is completed (you have already brought the souvenirs).
The imperfective counterpart привозил would imply a repeated or ongoing action rather than a single completed event.

Why is the form привёз masculine singular? What form would a female speaker use?

In Russian past tense, verbs agree with the subject in gender and number. Привёз is masculine singular, so it indicates that ты refers to a male speaker. A female speaker would use привезла instead of привёз.

Why is ты used instead of вы, and how would the sentence change if we switch to вы?