If you meant, "how is Gildor related to Finrod?", there is no easy answer. Gildor Inglorion translates as 'Gildor son of Inglor'. Inglor was the original name of Finrod, however, by the time FotR was published the name 'Finrod' had been replaced with 'Finarfin' and 'Inglor' had become 'Finrod'. If this editorial change had been made in later editions of FotR, Gildor's title should have read 'Gildor son of Finrod of the House of Finarfin'.

Unfortunately, this raises more questions than it answers, since we know from HoME that Finrod never had a son named Gildor (unless this was a nick-name such as Gil-galad, and Gildor's true name was something different).