"Nein, es ist niemand da."
"es ist" can mean "there is". It's not tricky to tell it apart from "it is" when you see the context so it probably won't confuse you much.
Later on, watch for "es gibt", "it gives". It also translates as "there is/are", but there are some distinctions in the usages that we don't make in English.
yup true why is 'es' in the sentence ? i have no i idea but maybe because it con insides with 'Somebody' meaning a person so 'es' is to pharse 'Somebody' either he/she.
I dont know but thought about and tried to answer. :/
"es" hasn't been taught to us as "there" yet, they goofed here, but I guess you learn by your mistakes, but this could confuse a beginner.