Question

there is，there are，there was，there were,have,has,had的用法

Answer 1

There is + 单数名词， 用于一般现在时 There is a book on the desk.
There are +复数名词， 用于一般现在时，There are some books on the desk.
There was + 单数名词， 用于一般过去时 There was a book on the desk just now.
There were+复数名词， 用于一般过去时 There were some books on the desk just now.
没有there have/has/had 但是有there have been/ has been/ had been 分别对应现在完成时和过去完成时。

单独用have has had 主语就不能再是there了
I have a book.
He has a book.
We had much money last year.