Il y a versus il y en a
Can someone please explain to me when it is right to use il y en a rather than il y a? Is it the difference between singular and plural nouns because it doesn't quite work with English translations e.g. Il y a du monde
"Il y a" can mean "there is" or "there are"
No, "en" is not used that way. Scroll down past the use of "en" as a preposition to its use as a pronoun. http://dictionary.reverso.net/french-english/en It is an indefinite amount.
So you will say "Il y a beaucoup de gens." or more commonly "Il y a du monde." to mean "There are a lot of people,
"Il y en a plusieurs." would mean "There are several of them" Whenever you could put "of them" or "of it", even though you usually don't have to in English; in French that prepositional phrase is replaced with the pronoun "en" before the verb.
Often "il y en a..." is translated as "There are some..."
"il y en a marre." is translated with "We are fed up." but you could see that you are fed up with something so you might say "We are fed up with it." or "We are fed up with them." and "en" in French covers that prepositional phrase.
"J'en ai besoin." means "I need some of it." or "I need some of them." which we may simply translate as "I need some."
"J'en ai assez." means "I have enough of it." which again we might shorten to "I have enough!"
"J'en ai peur." is usually translated to "I am afraid so." Try explaining to someone who does not understand English what "so" means there. Here it could be "I am afraid about it." technically in French although in English we would prefer to say "I am afraid that it is so." I suppose you could be afraid about it being so.
J'en ai parlé.. is "I talked about it."
"J'en ai pour un demi-heure." is translated as "It'll take me half an hour." but you realize that they are talking about something that is not mentioned. "It'll take me half an hour for that."
I hope you are starting to get the idea of an indefinite "something" that may be in a prepositional phrase.
"Il n'y a pas" = "There isn't" or "There aren't"
"il n'y en a pas" = "There isn't any (of it)." or "There aren't any (of them)."