c'est vs il est
Throughout all the exercises there are places where c'est and il est are each translated as
it's | this is | that is
At other times, they are not interchangeable. What's the rule?
C'est (ce + est) literally means "this is"/"that is".
Il est literally means "he is" (note that there are only two genders in French, there is no literal "it").
Generally, "c'est" is used when you're showing something, presenting, or pointing at it. For example, when introducing your parents to your friends you would say: "C'est ma mere et c'est mon pere".
"Il est" is used when you are talking about someone or something, usually introduced in a previous sentence. It is not uncommon to introduce something with "c'est" and then continue to describe it with "il est". For example: "C'est mon pere. Il est un grand architecte."
I hope this clarifies it for you.
I think Duolingo's context-free translation exercises are making a muddle of this as most of the time you can't tell whether a sentence is designed to be a presentation or a third person reference.
I wish they would clean it up throughout the lessons, so there's less distraction when trying to learn or refresh my knowledge of other concepts.