Greek in Greek is spelled ellenika and written ελληνικά.
Its ελληνικ-ος/η/ο/α (elinik-os/i/o/a) depending on the gender of the noun. In that order he/she/it/plural If Greek is used for a person from Greece its Ελληνας (helinas male) or...
You use the Greek alphabet.
εκεί , ekei [ek-EE]
Τι [Tee]