What does 'y' mean and how can I use it?

Y is a pronoun which is used to refer to a place which has already been mentioned, for example 'en ville'. It is not always translated in English but it must be included in French. For example, Vous allez en ville? Oui, nous y allons. = Are you going to town? Yes, we're going there. 

It can also be used with verbs which take a. E.g. Tu joue au football? Oui j'y joue. 

Y is also used in some common phrases:

Il y a - there is / there are 

Vas-y! - go on!

Allons-y! - Let's go!