句子的主干是：
What was not enough to do sth.
“什么”不足以让某人做某事.
What the Englishman showed to the waiter是主语从句,英国人向服务员所描述的东西；
make the waiter understand him correctly.是“make sb.do sth.”让某人做某事,
让服务员很好地理解.