Let's talk about "It"

(1) "This is my favorite restaurant. I love it!"
"It" = the restaurant. This is easy.

And everyone Japanese person knows expressions like (2) "It's raining," or "It is a hot day." But what does "it" mean in those sentences?

(1) and (2) are different forms of "it." In (1) "it" refers to a specific thing. In (2) "it" = situation. Here are some examples:

A. The earthquake and tsunami destroyed many homes. People were easy to get sympathy.
No: It was easy for people to get sympathy.
The situation: Immediately after March 11, 2011.

B. Runners are easy to get injured if the ground isn't level.
No: It's easy for runners to get injured if the ground isn't level.
The situation: running on unlevel ground.

C. The library was quiet so I could study there.
No: The library was quiet, so it was easy for me to study there.
The situation: the quiet library.

You're not going to master this, but you should be sensitive to (1) what a person makes happen versus (2) what a situation makes happen.

Let's use English well!