Already; (not) any more; by now — often used in phrases like 'already done' or 'no longer'.
もうご飯を食べましたか？
Have you already eaten?
彼はもうここにはいない。
He is no longer here.
もう終わったことだから気にしないで。
It's already over, so don't worry about it.
Soon; shortly; before long — indicating the near future.
もうすぐバスが来ますよ。
The bus will be here soon.
もうまもなく新しい曲が始まります。
The new song will start shortly.
Further; more; again — used to indicate an additional amount or repetition.
もう一度説明してもらえますか？
Could you explain it once more?
もう少し待ってください。
Please wait a little longer.
An interjection used to strengthen an emotion (e.g., exasperation, surprise) — like 'jeez' or 'come on'.
もう！時間を守ってよ。
Come on! Be on time.
もう、信じられない！
Geez, I can't believe it!