Which way/which direction; where — a polite pronoun used to ask about direction or location.
駅はどちらですか？
Which way is the station?
出口はどちらから出ればいいですか？
Which exit should I use?
こちらとあちら、どちらの道が早いですか？
Which road, this one or that one, is faster?
Which one (especially of two alternatives) — used to ask someone to choose between two options; casual form is どっち.
コーヒーと紅茶、どちらにしますか？
Coffee or tea — which would you like?
どちらの色がいいですか？（カジュアル）どっちがいい？
Which color do you prefer? (formal) Which do you like? (casual)
二つの案、どちらが現実的だと思う？
Which of the two proposals do you think is more realistic?
Who — a polite way to ask about a person (as in どちら様ですか?).
失礼ですが、どちら様ですか？
Excuse me, who is this? / May I ask who is calling?
お電話ありがとうございます。どちらにご用件でしょうか？
Thank you for calling. Who are you calling about / how may I direct your call?