Visualizations & Workbooks are a key component of the App Insights experience. They enable customers to monitor performance / failure trends & debug issues as they occur.
While performance data is critical to understanding the health of your application by itself it lacks the full context to help you understand why performance issues may be happening. Release Annotations are a simple way to add context & quantify the impact of an Azure DevOps release on your metrics.
Annotations can be automatically created by the Azure Pipelines build system. You can also create annotations to flag any event you like by creating them from PowerShell.
If your subscription has an Application Insights resource linked to it and you use one of the following deployment tasks, then you don't need to configure anything else.