1Which 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 is faster, this one or that one?
2Which one (especially of two alternatives) — used to ask someone to choose between two options; the 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?
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?
どっちが好き？（カジュアル）／どちらがお好みですか？（丁寧）
Which do you like? (casual) / Which do you prefer? (polite)
3Who — 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, may I ask who you are?
お電話ありがとうございます。どちら様でしょうか？
Thank you for calling. May I ask who's calling?