What's the difference?

How I can get to know when I should use "it", when "that" and when "this".

I am never sure if I'm using the correct word in sentence like that/it/this/wroten below?

1) It's not me / that's not me /
2) It's my sister / this is my sister / that's my sister
3) I'm sorry to hear that / it
4) It's simple / that's simple / this is simple
5) Let me explain it/that/this
6) It's / that's / this is quite impossible
7) Really? It's / that's / this is great
8 ) it / that / this sounds terrible
9) It's / that's / this is my favourite book

If I make mistake confusing it with that or this could it change the meaning of the sentence a lot?
See It vs that

The difference is in the translation to your language, but in english they can all be used and they all mean almost the same.
 CalifJim's reply was promoted to an answer.