Tutoring English, common constructions can cause review. The tutor mentions using “it” as a subject.
Speaker A: What’s the weather?
Speaker B: It’s raining.
Speaker A: How can you tell someone is lying?
Speaker B: It’s easy to tell.
In Scenario 1 above, “It” may refer to the weather itself: The weather is raining. Yet, you seldom hear The weather is raining.
In Scenario 2, “It” may refer to the fact that someone is lying: The fact that someone is lying is easy to tell.
Such use of “it” can be referred to as a “dummy” subject: the subject itself isn’t thought of, yet the sentence’s meaning is clear.
Source:Oracle Tutoring by Jack and Diane, Campbell River, BC.