以下是《牛津高级词典》对here开头的句子的解释：

used when you are giving or showing something to somebody.

用于你将一样东西递给某人或向某人介绍某个东西时。

Here you are. 给你。（将某东西递给某人的同时说这句话。）

Here's the money I promised you. 这是我向你许诺过的那笔钱。

Here's a dish that is simple and quick to make.这是一道简单快捷的菜。

Here is your opportunity.这是你的机会/你的机会来了。

Here comes the bus. = The bus is coming!

I can't find my keys. Oh, here they are. 哈，钥匙在这儿。

Here we are (= we've arrived).

there be存在句就不用解释了吧。