The basics
AWS credits vs AWS Free Tier
The Free Tier is small and for everyone. Credits are larger and you apply for them.
The AWS Free Tier is open to every new account. It gives a small amount of usage for free, enough to test services or run a tiny app, with limits on each service.
AWS credits are a dollar balance you apply for. They cover far more usage, apply to most services and are aimed at startups, migrations and specific projects.
You can have both. Free Tier usage is counted first, and credits then cover the rest of the eligible bill.
Questions
Is the Free Tier enough for a startup?
Rarely beyond the prototype stage. Once you have real users, credits make a bigger difference.
Prices and credit amounts are estimates and may change. Check AWS for current terms.