Relative pronouns are used to relate two clauses which share a common word.
For instance, consider the two following English sentences:
“The man is standing there”; “The man is my brother”.
These sentences can be combined by using a relative pronoun:
“The man who is standing there is my brother.”
The relative pronoun “who” related the common factor of both
sentences: “the man”. The pronoun “who” has the antecedent “man” (it
refers to “man”). The entire relative clause “who is standing there” is
like an adjective in this case.