The word "a" is used in different parts of a sentence.

Question

In the sentence "Está a dos cuadras de aquí", why is the "a" there?

Answer 1

"A" is definitely not used randomly in a sentence.

There are specific rules that guide it's usage, just like all grammar. Here is a link to a website that will help you learn how to correctly use "a" when communicating in Spanish. It is quite fascinating... link text

Answer 2

It is part of the expression. Sometimes that is the only reason. However, I have always thought of it as "at," and it is like saying, you are at "this point" from here. Another way to think of it: In English we say, "you are two blocks AWAY from here." It's similar to that, thought the "a" isn't optional like in English.