Hi Bill, 

You might find Chris' simple answer on when to use 'y' and 'en' useful -

https://french.kwiziq.com/questions/view/y-et-en#:~:text=Y%20and%20en%20are%20used,few%20lessons%20on%20this%20topic.

 

As for when to use the direct object pronoun 'le' or the indirect object pronoun 'lui', you will need to study the following lessons -

Using lui/leur = him or her/them (French Indirect Object Pronouns)

Using le/la/l'/les = it/him/her/them (French Direct Object Pronouns)

Hope this is helpful!