The "y" comes before the infinitive, similar to other pronouns. In the absence of the infinitive, it comes before the conjugated verb.

Je vais les rencontrer.
Je dois lui en parler.

In a frequently asked question, I found out that when using the ‘futur proche’ the pronoun ‘y’ is placed between the verb and the infinitive. For example ‘Je vais y aller’.

Thanks Chris. 

Helen,

The short answer is that the verb rêver takes the preposition "de" when we want to say we dream about/of something, and "de" is replaced by the pronoun "en".

Elle rêve de son père -> Elle en rêve.

It's simply because the lesson is about the pronoun "y". You're supposed to practice its use. 

-- Chris. 

In general, you are doing something very tempting when learning a foreign language, but something you can never do: you can never take an English sentence, translate each word with a dictionary, and end up with a correct foreign-language sentence. That's just not how grammar works. Foreign languages not only have different lists of words--they have different ways of putting words together into sentences.

There is a famous book where someone tried to go the other way: he took French sentences and looked up the matching English words in a dictionary. The results were pretty comical:

https://en.wikipedia.org/wiki/English_As_She_Is_Spoke

Hi Kalonde! It's more likely that you are hearing "Il en a" rather than "Y en a". They sound similar to our non-french ears when spoken fast, so it get us puzzled sometimes!