We use our background knowledge about the world and how it works to help us understand everything. Not only do we use different types of knowledge in comprehension, but this is applied in complex ways. There is no fixed way in which this knowledge is applied. Listeners have expectations about what they are hearing, and they use whatever knowledge seems relevant. Any relevant information might be used.
Comprehension is basically a guessing game.
Not all the necessary information is clearly stated. We use our knowledge to make inferences about the meaning. We don't always listen to every word, but make inferences based on the 4 types of knowledge. Comprehension is not understanding what words mean, but is understanding what speakers mean. Not everything is clearly stated, and it is often necessary to figure out the real meaning.