Auxiliary expressing a conditional: 'if (it is the case that)...' Used to state a hypothetical condition.
明日雨なら、ピクニックは中止です。
If it rains tomorrow, the picnic will be canceled.
学生なら学割が使えますよ。
If you are a student, you can use the student discount.
彼が来るなら、予定を変えましょう。
If he's coming, let's change the schedule.
Auxiliary meaning 'as for' or 'with regard to'—used to limit the topic or frame a comment.
映画なら、先週の作品が面白かったよ。
As for movies, last week's one was interesting.
田中さんなら、連絡先を知っているはずだ。
As for Mr. Tanaka, he should know the contact information.
Colloquial conjunction meaning 'if that's the case' or 'if so' (similar to それなら).
もう終わったなら、帰っていいよ。
If it's already finished, you may go home.
それなら、別の店に行こうか。
If that's the case, shall we go to another shop?
値段が高いなら買わないほうがいい。
If the price is high, it's better not to buy it.
Used to mean 'if possible' or 'if circumstances allow'—as in 'if you can/if it's possible'.
時間があるなら、手伝ってもらえますか。
If you have time, could you help me?
できるなら明日までに終わらせてほしい。
If possible, I'd like it finished by tomorrow.