Metaphor forms part of our way of thinking, of understanding the world. At times, it lexicalizes (that is, it becomes very common), and we are not aware that we are using a metaphor: Life is not a bed of roses.
We base on previous models to produce communicative units, and a transmitter, a receiver and a channel are necessary. Nevertheless, it does not imply that these units are not creative.
In a metaphor there are two terms or planes: the real one (my husband) and the evoked or imaginary one (ox). There is, then, some similarity between the two terms. If only the evoked plane appears, we have a pure metaphor: The pirate of his heart (that is, her love) destroyed his life, and if both terms are present, impure: Her love was the pirate of his heart, which destroyed his life.
Metonymy expresses contiguity, possession, degree, proximity... The important thing here is to belong to the same group, species, etc. Synecdoche can be included in metonymy, and it refers to the substitution of the part for the whole or of the whole for the part.