B is correct because enabling the Cloud Spanner API is the initial step required to use Cloud Spanner. This action allows your Google Cloud project to interact with the Cloud Spanner service. Before any configuration or setup of the instance, the API must be enabled to ensure the service is available for use.

A is incorrect because while configuring a Cloud Spanner instance to be multi-regional is important for global availability and low-latency access, it is not the first step in the creation process.

C is incorrect because Cloud Spanner is a managed service that does not require a VPC network for operation. Creating a VPC network with subnetworks is unrelated to the initial setup of a Cloud Spanner instance.

D is incorrect because the project creator automatically receives the owner role, which includes permissions to create Spanner instances. Assigning the Cloud Spanner Admin IAM role is a step for managing permissions but not the first step in instance creation.