Coggan power zones from your FTP, and heart-rate zones from your threshold or maximum heart rate — the intensity bands to train and pace to. Enter what you know; estimate the rest.
Power zones use Dr Andrew Coggan's seven-zone model — each zone is a percentage band of your Functional Threshold Power (FTP), the power you could hold for roughly an hour. If you've done a 20-minute test instead, FTP is taken as 95% of your 20-minute power.
Heart-rate zones work from your lactate threshold heart rate (LTHR) — the Coggan/Friel five-zone model — or, if you don't know your LTHR, as percentage bands of your maximum heart rate. LTHR-based zones are the more reliable of the two; HR lags effort and drifts with heat, fatigue and caffeine, so treat any HR zone as a guide rather than a hard limit.
This tool deliberately won't estimate your maximum heart rate from your age (the “220 − age” formula): it's wrong by 10–20 bpm for a great many people. Enter a heart rate you've actually measured.
The percentage tables and the full reasoning are documented in this tool's research.md.