Start a conversation: describe the lesson you want (topic, grades, country, characters) and paste any design or notes.
On your machine: printed once at startup and kept in the studio's .env as STUDIO_TOKEN. On the dev server: in AWS Parameter Store (the README says how to read it). Kept in this browser only.
.env
STUDIO_TOKEN
The engine reuses every stage before the one you pick and runs that stage and everything after it again. On the mock provider every option is free.