What’s the difference between a metaphor and a symbol?

They're related, but generally a metaphor is used to draw a comparison between two distinct objects, whereas a symbol is used a stand-in for a much more complex, and generally more abstract, idea. In literature, a metaphor would typically be used in a specific instance to compare two objects, but a symbol would be used throughout the work as a major part of the theme.

Taking into account the explanation, it seems to me the animals in the story "Animal Farm" could be different symbols.

If so, what about an example as ti metaphor?