If you get on like a house on fire, that's an idiomatic expression meaning that you really are good friends, you don't argue, you're just the best friends ever, right? get on like a house on fire.
如果你 get on like a house on fire,这一个语表达,意思你们真的好朋友,你们不吵架,你们最好的朋友,相处融洽。
So again, sometimes your understand all the words that you hear but you're not gonna understand the meaning, because it might be an idiomatic expression that you're unfamiliar with.
They will include idioms, sayings, phrasal verbs, so brush up on your idiomatic expressions, don't " throw in the towel" , and you will " sail through" the exam with " flying colours" .