It’s is the contracted form of IT IS --> The “I” falls and it is replaced by an apostrophe --> It’s

e.g. It’s a beautiful day

Its is the possessive adjective or possessive pronoun used to indicate that something belongs to IT

e.g. Look at its tail!

There is the contracted form of They are --> The “A” falls and it is replaced by the apostrophe --> They’re

e.g. They’re brothers

Their is the possessive adjective used to indicate that something belongs to THEM

e.g. Their house is big

There can be used:

-as an adverb to indicate that something is “in that place”

-as a pronoun, e.g. There is a cat

-as a demonstrative adjective, e.g. Look, it’s there!