Guest access allows attendees to quickly and easily join meetings without going through a signup process. Guests can participate in meetings (view the agenda, suggest topics, vote), but they cannot create or run their own meetings.
Guest access is most useful for people you invite outside your team or organization. They can join quickly and easily without creating an account. More advanced features (such as managing action items assigned to you) require that you sign in (create an account).
Only moderator accounts (trial or paid) can create and moderate meetings. Guest and Attendee access are free.