Free and genuinely free — an email or Google account, no card, nothing to install. Start in the playground rather than with a key — though Groq's docs never quite say the playground runs without one, so you may need to make a key once you are signed in.
The free plan gives you nothing to spend. It caps how often you can ask. It counts requests and tokens (chunks of text, roughly three-quarters of a word) per minute and per day; hit a cap and requests fail until it resets. Caps cover your whole organisation, not each key, and only the limits page in your console settings is current — published numbers change.
You probably won't pay. Usage beyond that is currently priced per million tokens, cents rather than dollars for the smaller models — check the pricing page. You'd upgrade for real users hitting the caps, for batch or flex processing, or for the spend cap under Settings, Billing, Limits, which is paid-plan only.