Explanation
Work order line items are used to track individual products or services that are part of a work order. By creating a work order line item for each installed product that needs servicing, the system can track the status and completion of each product separately.
References:
https://trailhead.salesforce.com/en/content/learn/modules/field_service_basics/field_service_work_order_line_ite

Explanation
Field Service Lightning Admin Permissions are required to set up new territories, define new schedule policies, and control settings on the Gantt chart. These permissions allow users to access and modify field service settings and objects.
References: https://help.salesforce.com/s/articleView?id=sf.fsl_permissions.htm&type=5

Explanation
These are two actions that can help ensure that the technician who performed a customer's initial installation is also assigned to subsequent service calls. A preferred resource is a resource that has a preference or affinity for working with a specific account or service territory. A preferred resource service objective is a service objective that prioritizes resources that are preferred for an account or service territory. By adding the technician as a preferred resource on the account record, and adding the preferred resource service objective to the scheduling policy, the system can assign the technician to future service appointments for that account.
References: https://help.salesforce.com/s/articleView?id=sf.fsl_preferred_resources.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.fsl_service_objectives.htm&type=5