well; properly; skillfully — used to say that something is done competently or adequately.
彼女はピアノをよく弾く。
She plays the piano well.
このアプリはよくできている。
This app is well made.
説明を読めばよく分かる。
If you read the instructions you'll understand well.
often; frequently — indicating repetition or frequency.
彼はよく海外に出張する。
He often goes on business trips abroad.
この店にはよく来ますか？
Do you come to this shop often?
よく雨が降る季節だ。
It's a season when it often rains.
used to express relief or appreciation (e.g., 'I'm glad you...'; 'well done').
よく来てくれた、話がしたかったんだ。
I'm glad you came — I wanted to talk.
よく見つけてくれたね、助かったよ。
I'm glad you found it — that helped a lot.
used to express indignation or disbelief (e.g., 'How dare you...'; 'I can't believe you...').
よくそんなことが言えますね。
I can't believe you can say such a thing.
よくもそんな嘘がつけるね。
How can you tell such a lie?