John 1:12

ὅσοι δὲ ἔλαβον αὐτόν, ἔδωκεν αὐτοῖς ἐξουσίαν τέκνα θεοῦ γενέσθαι, τοῖς πιστεύουσιν εἰς τὸ ὄνομα αὐτοῦ,

ὅσοι relative pronoun "as many as"

δὲ post positive conjunction "and" or "but"

ἔλαβον verb aorist active indicative 3rd plural from λαμβάνω "received"

αὐτόν personal pronoun accusative masculine singular "him"

ἔδωκεν verb aorist active indicative 3rd singular from δίδωμι "he gave"

αὐτοῖς pronoun dative plural "to them"

ἐξουσίαν noun accusative feminine singular "authority"

τέκνα noun nominative neuter plural "children"

θεοῦ noun genitive masculine singular "of God"

γενέσθαι verb aorist middle infinitive from γίνομαι "to become"

τοῖς defininte article dative masculine plural "the"

πιστεύουσιν verb present active participle dative masculine plural (note the attributive position of this participle. It is describing the "them" of αὐτοῖς.)

εἰς prepostion with accusative case "in" or "into"

τὸ definite article accusative neuter singular "the"

ὄνομα noun accusative neuter singular "name"

αὐτοῦ personal pronoun genitive masculine singular "of him"

Rough Translation:

as many as but received him he gave to them authority children of God to become the believing in the name of him

Smooth Translation:

But as many as received him, to them he gave authority to become children of God, the ones believing in his name.