In the grammar notes under the "phrases" lesson, it has a section on "The Impersonal Expression Il Y A".
<<Impersonal expressions are phrases where there isn't a real subject. For instance, in the phrase "It is snowing" (Il neige), "it" doesn't refer to anything. It's a dummy subject that exists just to maintain the sentence structure.
One of the most common impersonal expressions is il y a, which is an idiom for "there is" or "there are".>>
And in the grammar notes under the lesson for "etre/avoir," it has a section on "C'est or Il Est?".
<<When describing people and things with être in French, you usually can't use a personal subject pronoun like elle. Instead, you must use the impersonal pronoun ce, which can also mean "this" or "that". Note that ce is invariable, so it can never be ces sont.>>
I didn't copy the entire grammar note, but I hope this helps! I'm just learning it, too, so I just stuff it into my head and hope it eventually sticks and makes sense.