Where the forms of the relative correspond with the definite article, the relative is accented, e.g., ἥ, οἵ, αἵ.
The meanings of the relative pronoun are as follows. In the nominative case, who, which, what, in the accusative case, who, whom, which, what. The genitive pronoun is translated as of whom, of which, whose, while the dative: means to, for, by, with which/whom.
The relative pronoun agrees with its antecedant in gender and number. Its case depends on its function in the relative clause.
ὁ παῖς, ὅν παιδεύω, ἔχει ἵππον.
The child, whom I teach, has a horse.
The relative pronoun ὅν agrees with 'child', and is in the accusative case as the direct object.
ὁ παῖς ὅς πέμπει δῶρον ἀγαθός ἐστίν.
The child who sends a gift is good of the relative clause.
The relative pronoun ὅς agrees with 'child', and is in the nominative case as the subject of the relative clause.
ἡ κώμη, ἐν ἥ μένομεν, μικρά ἐστίν.
The village in which we are staying is small.
The relative pronoun ἥ agrees with 'village', and is in the dative case as the object of the preposition in the relative clause.
ὁ παῖς, οὕ ὁ δοῦλος λέγει, ἀγαθός ἐστίν.
The child, whose slave is speaking, is good.
The relative pronoun οὕ agrees with 'child', and is in the genitive case denoting possession in the relative clause.