Я на первом курсе. It's my first year. I'm a freshman.
Я на втором курсе. It's my second year. I'm a sophomore.
Я на третьем курсе. It's my third year. I'm a junior.
Я на четвертом курсе. It's my fourth year. I'm a senior.
Я на пятом курсе. It's my fifth year. I'm fifth year senior.