。
Ken, a graduate student, went to America last year.
Literal
Graduate-student [genitive-の] Ken [topic-は] last-year America [target-に] went.
Standard past-tense introductory sentence. 大学院生 ('graduate student') is a compound: 大学院 ('graduate school') + 生 ('student'). The の links 大学院生 to ケン as an appositive, giving 'Ken, the graduate student.' Otherwise straightforward. 行った is the basic past tense of 行く.