I want to know when to use en and when to use y. The explanations are NOT clear to me. Can someone help?

Hi Nancy, 

This is not easy to answer in the Q&A. 

Have you had a look at the following Kwiziq lesson? -

Y can replace à + thing / object / location (adverbial pronoun)

Also, you might find this answer to a similar question useful?

https://progress.lawlessfrench.com/questions/view/y-vs-en

Hope this helps!