Everyone currently has unrestricted access to your BigQuery warehouse and uses it without documentation. To discover what users are doing, what should you do first?

To understand current user activity in BigQuery, reviewing Stackdriver Audit Logs is the most direct and effective first step. Audit Logs record administrative activities, data access, and system events, providing detailed information about who accessed what data, when, and how. This directly addresses the need to "discover what users are doing." Getting IAM policies for each table shows who has permission to access data, not who is actually accessing it or what queries they are running. Stackdriver Monitoring for query slots shows overall resource consumption but doesn't detail individual user actions or specific data accessed. The Cloud Billing API provides cost information, which is irrelevant to understanding user behavior or data access patterns.