John 1:18

θεὸν οὐδεὶς ἑώρακεν πώποτε· ὁ μονογενὴς υἱὸς ὁ ὢν εἰς τὸν κόλπον τοῦ πατρός, ἐκεῖνος ἐξηγήσατο.

θεὸν noun accusative masculine singular "God"

οὐδεὶς adjective nominative masculine singular "no one"

ἑώρακεν verb perfect active indicative 3rd singular from ὁράω (I see) "he has seen"

πώποτε· adverb "at any time"

ὁ definite article nominative masculine singular "the"

μονογενὴς adjective nominative masculine singular "only begotten/only born"

υἱὸς noun nominative masculine singular "son" (note: There is major support for Θεός here in place of υἱὸς. The UBS apparatus shows less support for υἱὸς in fact. There certainly are theological implications here.)

ὁ definite article nominative masculine singular "the"

ὢν present active participle nominative singular masculine from εἰμί (I am) "the one being"

εἰς preposition with accusative "in"

τὸν definite article accusative masculine singular "the"

κόλπον noun accusative masculine singular "bosom"

τοῦ definite article genitive masculine singular "the"

πατρός noun genitive masculine singular "father"

ἐκεῖνος pronoun "he"

ἐξηγήσατο verb aorist middle deponent 3rd singular from ἐξηγέομαι ( I make known) "he has made known" (He has exegeted)

Rough Word-by-word:
God no one has seen at any time the only begotten son the the one being in the bosom the of Father this one/he he has made known

Smooth Translation:
No one at any time has seen God. The only begotten son (or God) being in the bosom of the Father has made Him known.