什么时候用过去完成时?什么时候用现在完成时?什么时候用过去时?

什么时候用过去完成时?什么时候用现在完成时?什么时候用过去时?
拿新概念2的第14课做例子
I had an amusing experience last year.
After I had left a small village
in the south of France,
I drove on to the next town.
On the way,a young man waved to me.
I stopped and he asked me for a lift.
As soon as he had got into the car,
I said good morning to him in French
and he replied in the same language.
Apart from a few words,
I do not know any French at all.
Neither of us spoke during the journey.
I had nearly reached the town,
when the young man suddenly said,
very slowly,"Do you speak English?'
As I soon learnt,he was English himself!