Students registered with the GitHub Student Developer Pack receive one allocation of $312 in Heroku platform credits, which burns down at $13 per month for 24 months. Credits can be spent on any Heroku product, including Eco dynos, Heroku Postgres and Heroku Key-Value Store, but not on third-party add-ons.
A valid credit or debit card must be on file, and usage above $13 in a month is charged. Unused monthly credit does not roll over, and credits start on the first day of the month you are approved, so applying early in the month gets you the most value.