それ + は / が / を / も / の
それ means "that" or "that one": a thing near the person you are talking to, and not near you. It is a noun, so は and the other particles follow it directly.
It is one of a set of four:
The word changes with who is speaking: you ask about the thing in the other person's hand with それ, and they answer with これ.
English "that" covers both. Japanese splits it by where the listener is: それ is near the listener, あれ is far from the listener too. For the bag beside the person you are talking to, say それ. For a mountain you are both looking at, それ is wrong and the word is あれ.
それ stands alone. In front of a noun the word is その: ×それ本 is wrong.
を, も and が follow それ the same way は does.
English puts "it" in sentences where Japanese leaves the subject out, and putting それ wherever English has "it" sounds stiff. After きのうえいが映画をみました見ました, "it was interesting" is おもしろかったです面白かったです, not それは面白かったです.
These go beyond pointing at a thing you can see.
それ also points back at what the other person has just told you, like "that" in "that's good".