I am student 나는 학생이다. I was student 나느 학생이었다. I will be student 나는 학생이 될것이다. :)

Just remember that the English verb "to be" is represented by two different verbs in Korean: one for equality: 이다; and one for existence: 있다. And if you want to say something like "I am happy (or any other adjective)", you need to use the respective descriptive verb in Korean.