A typical guide opens with a short script for introductions, lists each question with optional follow-up prompts, and notes which competency every question is meant to test. It usually sets a time budget per section and includes a rating scale with examples of weak, adequate and strong answers. Interviewers fill it in as they go, so notes and scores are captured in the same place.
Without a guide, interviews drift towards whatever the interviewer finds interesting, and candidates end up compared on different evidence. A shared guide makes panels easier to calibrate, helps new interviewers run a fair conversation and leaves a record of why each score was given. Reviewing the guide after each hiring round keeps questions current and tied to the role.