There are a few different ways of using the word "angel." First, there's the belief that an angel is a person who has died and gone to heaven. Some angels have the power to return to earth and protect human beings from evil. Angels usually have wings and can fly. Whether you believe these things or not, you will hear people talk about angels.
Beatrice says that her guardian angel is watching over her.
Some angel must have protected the refugees from disaster.
There's an angel watching over your shoulder.
An angel must have earned his wings today. (This means that one person or group of people were saved from a disaster.)
You will also hear the word "angel" used when talking about a person who is alive here on earth. In this case, it means that the person is nice or well-behaved.
Martha was a little angel the entire time her mother was gone.
Thanks for helping me. You're an angel.
Matthew has the voice of an angel.
An angel investor appeared from nowhere and saved the company from ruin.