Learn Spanish (Latin America): Si tienes un turno, te atienden rápido. - If you have an appointment, they serve you fast.

While cita is widely used for appointments, in many parts of Latin America, turno is the everyday word for a medical, salon, or bureaucratic appointment. Cita can sometimes imply a romantic date or a formal business meeting.

Who is the "they" doing the action in te atienden?

Here, atienden (they serve) is used as an impersonal "they". Just like in English when we say "they serve you fast at that office," it doesn't refer to specific people, but generally to the staff working there.

Why is the word for "fast" rápido and not rápidamente?

In spoken Spanish, it is very common to drop the -mente ending and just use the adjective rápido to mean "quickly". You can say rápidamente, but rápido sounds much more natural and conversational here.

Could I use the future tense and say te atenderán (they will serve you)?

Yes! However, using the present tense for both halves of an "if" sentence (tienes and atienden) is a very common way to state a general fact or a reliable rule in Spanish.