5 ways how to use " Could"

Could has a lot of meaning.
I'm confused how to use "could" sometimes.

Less sure than can

• You could give her a present.
• We could go to the movie.

Unrealistic

• This is really good place. I could stay forever.
• I'm exhausted. I could sleep for 3 days.

Similar to might and may

• Maybe I could stay there.
• I could apply for it.
• We could go to the movie.

It was possible but didn't happen

• Why did you stay home yesterday? You could have come to the party last night.
• Why did you ask me that? I could have given my ticket.
• Why did you walk? You could have taken a taxi.

Something would not be possible

• Couldn't be better.
• I couldn't live there. I don't like a small city.
• I couldn't get up at that time.
• They couldn't have been helpful.

Harry Potter and the Chamber of Secrets (US) (Paper) (2)