They are all used in several different ways. Let's just look at how they are used to point back to something you've already said. Use "it" to point back at a single word. Use "that" to point back at a whole sentence, idea, or situation. I like this dog. *It's* a good dog.// it= the dog I like this dog. *That's* good, because my girlfriend likes it too.// that= the fact that I like the dog As I said, there are several other ways we use each of thyese words. but you can start here.

I don't know Portuguese. In Spanish, "este" and "ese" are exactly the same as the English "this" and "that," so probably Portuguese "este" and "esse" are, too. Can you explain the difference between "este" and "esse?" That is the difference between "this" and "that." Like "this" and "that," "it" is a pronoun. A pronoun refers to a longer word or phrase. You can replace a pronoun with the word or phrase it stands for. Unlike "this" and "that," "it" does not have any feeling of distance. It is easiest to explain by comparing it to "he" or "she." "Linda is at the computer. She is using Excel." We can rewrite the second sentence as "Linda is using Excel." "She" refers to "Linda." "He" refers to a man (or a male child or a male animal). "She" refers to a woman (or female child or female animal). For everything else, we use "it." "It" can refer to real things, or ideas, or things we have just said. The knife is on the table. It is sharp. Brazil is a country. It is large. Beethoven's Ninth Symphony is a piece of music. It is about an hour long.

it is often about distance from the speaker, but not always. read the link below and then ask question on anything you are having difficulties with. https://dictionary.cambridge.org/grammar/british-grammar/writing/it-this-and-that-in-paragraphs

There are units and units of grammar books on these issues. I recommend you post real sentences and ask why e.g. "it" was used or not used.