There is 和 there are 是 there be句型 的现在时，表示某人事物的存在，“有……”。
There is 用于单数（可数）名词和不可数名词。

There are 用于复数（可数）名词。 

办公室里有五个人。—>
There are five people in the office.
客厅里有一台电视。—>
There's a television in the living room. 
冰箱里有一些牛奶。—>
There's some milk in the fridge. 

关于some

复数可数名词，可以用准确的数量，也可以用some表示不准确知道的数量：
There are five people in the office. 办公室里有五个人。 
There are some people in the office. 办公室里有一些人。

不可数名词，也常搭配some：
There's some milk in the fridge. 冰箱里有一些牛奶。
There's some money in my wallet. 我的钱包里有一些钱。

单数可数名词，不能搭配some，可搭配a/an，the或者限定词等：
There's a woman in the shop. 商店里有一个女人。
There's the woman who works in the hospital. 有一个在医院工作的女人。
There's my sister in the photo. 照片里有我妹妹（姐姐）。