You can approach metaphor in many ways.
What line is taken here?
The material on this website is largely based on what has become known as Conceptual Metaphor Theory. Major proponents include the following (links take you to book descriptions): Kövecses; Lakoff & Johnson. Work inspired by this approach demonstrates how metaphor is not just a way of using words but also a way of perceiving, thinking, reasoning, and acting.
This approach has been adapted and extended. For example, Charteris-Black; Eubanks; Musolff, show how complex metaphors work in extended discourse.
Of great interest here is the use of metaphor "real time" in conversation and on-going dialog, for example Cameron.
Next: Steps in learning how metaphor works in everyday life