[kunitokotachi]

これ= this
それ= that
あれ= that (way over there)

Ex:
これはぺンです。= this is a pen.
それは机(つくえ)です。 = that is a desk.
あれは扇風機(せんぷうき)です。 = That over there is a fan.


The three below you connect with another noun.
この= this
その= that
あの= that (way over there)

このぺんは僕(ぼく)のです = This pen is mine.
その机(つくえ)は小さい(ちいさい)です。= That desk is small.
あの扇風機(せんぷうき)は古い(ふるい)です。= That fan over there is old.

Also,
Let's say someone said to you:
それを貸して下さい(かしてください)。Please let me borrow that.
and you didn't know exactly what so you wanted to ask them, "This?"
You can say, "これ？" or これですか？ but you wouldn't say "この？"