This is the 7459th most frequent Japanese word.
健太
"健太" is a Japanese male given name meaning "healthy" (健) and "plump/robust" or "great" (太).
The word 健太 indicates possession in this sentence, showing that the room belongs to Kenta.
すごい、健太の部屋はとてもきれいですね。
Wow, Kenta's room is very clean.
The word 健太 is used as part of a phrase indicating accompaniment, highlighting that Kenta is involved in the action.
健太と一緒に映画を観に行こう。
Let's go watch a movie together with Kenta.
The word 健太 represents a proper noun, specifically a person's name, used as the subject of the sentence.