When a series of words close to each other start or contain the same sound. An example is, 'The boy crept carefully along the corridor'.
When you use something to represent something else as part of a description. An example is, 'His eyes were awash with an ocean of emotions'.
When you use something as a comparison with something else as part of a description. The comparison is normally made using the words like or as. An example is, 'He was as quiet as a mouse'.
When a thing represents something else. An example might be using darkness to represent a secret, something hidden, or evil.