Idioms are peculiar. Even if one knows all the words that make one up, the meaning must be learned.

That is, understanding the meanings of "get" and "along" individually does not really help in deciphering that "get along" can mean "to be friends with".

Metaphors, on the other hand, create images in a reader's mind. If you know all the words that make up a metaphor, you have a good chance of getting the intended image.

"Joe and Sue are bread and butter together" is a metaphor for Joe and Sue's good relationship. (I just pulled that one out of my head; I know it sounds terrible.) So, if you know all the words (bread, butter, together, etc) and you come from a culture where people enjoy eating bread with butter, you can easily undertand the meaning of the metaphor.

More examples:

"I had my lunch." (Idiom. It means "I ate my lunch", rather than the literal "I possessed my lunch".)

"I wolfed my lunch." (Metaphor. I acted like a wolf with my lunch; I ate it like a wolf would.)

Does this help?

Anonymous

“My girlfriend is a bit of a tough cookie.  Metaphor or Idiom?”

Probably just an idiom, I guess...