He made his own decision - I had nothing to do with it.

had 是动词 have 的过去式，表示"有"或"经历"。 nothing 是代词，表示"没有任何事物"或"零"。 to 在这里是不定式符号，用于连接动词原形。 do 是动词，表示"做"或"执行"。 with 是介词，表示"与...一起"或"关于"。 had nothing to do with 是一个固定短语，意思是"与...无关"或"不参与"。