If we'd had the money, we'd have bought a new car.

if 是连词，意思是"如果"，用于引导条件状语从句，表示假设的情况。 we'd had 是 we had had 的缩写形式，第一个 had 是助动词，第二个 had 是动词 have 的过去分词，构成过去完成时态，表示在过去某个时间点之前已经完成的动作。 we'd have bought 是 we would have bought 的缩写形式，would have bought 是虚拟语气的结构，表示与过去事实相反的假设情况下的结果。