How to file if I was an unemployed full time student?

You probably don't file.   If you are somebody's dependent, they should claim the tuition credit for your education. 

But, there are exceptions.  If you have scholarships that exceed your tuition by more than $12,550*, you have taxable income to be reported.

Unemployment compensation is taxable income

If you are a student and are not claimed as a dependent by someone else (e.g. your parent) you may be eligible for the up to $1000 refundable American Opportunity (tuition) Credit. You must be at least a half time degree seeking undergraduate student.  Unmarried, full time students under 24 are not eligible.

*$12,550 Total income from all sources

If you did not have any income and can be claimed as a dependent then you do not need to file a tax return. You won't be able to claim the education credits if you can be claimed as a dependent and have no income.