Good morning! - is used to greet someone in the morning. (around 5am - 11am)

Good afternoon! - is used to greet someone during the noon or after that. (around 12pm to 3pm)

Good evening! - is used to greet someone during the sunset or after that. (around 4pm to 10pm)

Good night! - is used to depart from someone when the sun is already down. (around 8pm to 3am)

How are you? - is used to ask someone about their current wellbeing.

I'm fine thank you, and you? - is used to respond to "How are you?".

I'm pleased to meet you!- is used after introducing yourself. Now you're officially friends!

I'm sorry but I have to leave soon, it was nice talking to you. - is used to apologize before leaving.

See you soon! - is used to promise the other party that they will meet again.

Goodbye! - is used to bid farewell one last time before leaving and parting ways.

To feel under the weather - feeling unwell.

Ex: I think I'll call in sick today, I'm feeling a bit under the weather.

Once in a blue moon - something that doesn't happen frequently.

Ex: Her brownies are really delicious but she only makes them once in a blue moon.

Hang in there - don't give up

Ex: You're already halfway through the exam week, hang in there!

Your guess is good as mine - I have no idea

Ex: That's a really good question, your guess is as good as mine.