What happens initially when a computer joins a domain in Active Directory?

When a computer joins a domain in Active Directory, a computer account for that machine is created automatically in the domain's accounts database. This computer account is essential for the domain to authenticate the computer and manage its policy settings. It allows the domain to recognize the computer as part of its network, enabling centralized management, security, and configuration.

The creation of this computer account is a fundamental part of the Active Directory's functionality, as it maintains an identity for the computer within the domain environment, facilitating various interactions like user authentication and the application of Group Policies. This process streamlines the network administration by ensuring that once a computer is joined to the domain, it can follow the defined policies and access resources as governed by the network administrator, enhancing overall security and management efficiency.

In contrast, the other choices suggest actions that do not accurately describe what occurs during the initial joining process of a computer to a domain in Active Directory. For instance, creating a new group or deleting existing user accounts does not happen as part of the joining process. Additionally, automatically joining an administrative group would not be a standard procedure, as membership in such groups typically requires explicit permission and security considerations.