Then suddenly we saw a huge wave coming towards us.
主we,谓saw,宾a huge wave,时间状语then suddenly,coming towards us作wave的定语修饰成分
There was a terrible noise,and the wave seemed to come over the top of us ,but we didn't get wet at all.
需要分为三块分析,
第一块There was a terrible noise.there 为虚词,was后面的名词短语做真正的主语,即主a terrible noise,there be 表示存在
第二块and the wave seemed to come over the top of us.and连词,连接第一块和第二块,主the wave,系seemed,表to come over the top of us（不定式作表语）
第三块but we didn't get wet at all.but连词,连接第二块和第三块,主we,系动词get,表语well （形容词）,助动词didn't表示否定,at all 表程度.
I don't know how they did it.
主I,谓know（don't是助动词表示否定）,宾语从句how they did it中,they做从句的主语,did做从句的谓语,it做从句的宾语,how是引导词.