It appears that you receive a $100 credit if your school is a 'member' educational institution, or $30 if it is not. From what I can tell, all you need is to sign up with your school's email address to create an account. Based on my reading of their tos, you can use these credits towards AWS services.
From what I can tell, you are limited to using your credits towards these services.
You can add a promotional code to your AWS account by following these instructions:
Open the Credits page of the Billing and Cost Management console. In the Promo Code box, type the promotional code. In the box labeled Please type the characters as shown above, type the code. Choose Redeem.
It appears that you may need to have your .edu email address associated with your amazon account, but this is unclear.