Planner accounts are typically those responsible for planning the details of the service and/or leading teams that serve. Planners have a security level that determines what they can update in their church's account. Only Planners can be team leaders.
Helpers are typically the volunteers. Those that show up for a service to serve, and don't contribute to the planning, scheduling, or organizing of the service details. Helpers have access to details of services for which they are scheduled. Some Helpers can be given access to details of services even if they aren't scheduled for it.
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