There is/are表示某处有某物,there is +可数名词单数,或不可数名词如：there is a book on the desk.there is a book and two pens on the desk.(就近原则) there is water in the glass,There are+可数名词复数.there are books on the desk.
或表示时间的包含关系there are seven days in a week.很简单的,