Learn Swedish: Förstår ni oss? - Do you understand us?

Vi means "we" (the subject doing the action), while oss means "us" (the object receiving the action). Since "we" are the ones being understood here, we need the object pronoun oss.

Wait, is there no Swedish word for "do" in this question?

Exactly! Swedish doesn't use helper words like "do" or "does" to ask questions. You simply swap the subject and the verb. Instead of "Do you understand?", you literally say "Understand you?" (Förstår ni?).

Does ni mean "you" for one person or multiple people?

In standard modern Swedish, ni is the plural "you" (like "you all" or "you guys"). If you were asking just one person, you would use the singular pronoun du: Förstår du oss?

Why does the verb förstår end in -r instead of -ar or -er?

Most Swedish verbs add -ar or -er in the present tense. However, förstå (to understand) is a short verb that already ends in a stressed vowel. For these verbs, you just add an -r to make the present tense: förstår.