DOCS-8111 (#32793)

* DOCS-8111

Add Cloud Costs Explorer Documentation

Updated existing doc page to include more information on the side panel.

* Apply suggestions from code review

Co-authored-by: Rosa Trieu <107086888+rtrieu@users.noreply.github.com>

* [DOCS-8111] Incorporate feedback

* [DOCS-8111] Update image

* [DOCS-8111] Update link

---------

Co-authored-by: Rosa Trieu <107086888+rtrieu@users.noreply.github.com>
Co-authored-by: Bryce Eadie <bryce.eadie@datadoghq.com>

Author: 3 people

content/en/cloud_cost_management/reporting/explorer.md

@@ -44,7 +44,44 @@ Use the Cost Explorer to:
 
 4. Select a time range using the time picker to analyze costs over different periods (hour, day, week, month, or custom range).
 
-**Note:** When querying costs across multiple providers, resource-level tags are not available. To access resource-specific tags, filter to a single provider in your query.
+**Note**: When querying costs across multiple providers, resource-level tags are not available. To access resource-specific tags, filter to a single provider in your query.
+
+## Cost Change Summary side panel 
+
+Click any row in the table at the bottom of the Explorer to open the **Cost Change Summary panel** for that specific provider, service, or resource. The panel highlights what and who may be driving cost changes for the current period versus the prior period.
+
+The panel contains four general sections:
+- Cost change summary
+- Associated teams
+- Change details
+- Investigate further
+
+{{< img src="cloud_cost/reporting/cost-change-sidepanel.png" alt="The Cost Change Summary panel highlights what and who may be driving cost changes for the current period versus the prior period." style="width:100%;" >}}
+
+At the top, you can see the **total cost** for the current period and the dollar and percent cost change versus the prior period (**what happened**). 
+
+### Investigate the change
+
+Use the **Change Details** and **Investigate Further** sections to:
+
+- **Instantly identify cost anomalies**: Unexpected deviations in cost, calculated against historical data, are automatically highlighted in red, allowing you to focus your investigation on critical trends.  
+     
+- **Analyze Change Drivers**: Easily determine the cause of a cost change—whether it was driven by a change in **usage** (the count of resources) or a change in **unit price** (the cost per resource). For example, in the screenshot below, the change in spend is driven by a shift in unit price rather than usage---the resource count stays flat while cost per resource rises and falls, causing the overall cost change.
+
+{{< img src="cloud_cost/reporting/cloud-cost-spend-summary.png" alt="The change in spend is driven by a shift in unit price rather than usage—the resource count stays flat while cost per resource rises and falls, causing the overall cost change" style="width:100%;" >}}
+
+### Collaborate and monitor
+
+- **Contact the responsible team**:
+  - Review the **Associated Team(s)** section to identify which teams own the resources driving the cost change (inferred from tags like `team:shopist`). Follow up with the listed teams (for example, Shopist, Platform, Cloud-Networks) to gain full context for the change.
+  - Click **Send Notebook** to share the full cost investigation context directly with the team, allowing them to capture findings, add annotations, and track the investigation thread.
+
+- **Filter by tags**:
+  - Use **Associated Tags** to see all tags contributing to the cost line item.
+  - Click any tag value (like `account:demo` or a specific `aws_account`) to refine your search and filter the entire Explorer to show only resources with that tag.
+
+- **Create a monitor**:
+  - Set up a Cloud Cost Monitor to be alerted the next time a similar change occurs. Learn more about [Cloud Cost Monitors][8].
 
 ## Refine your results
 
@@ -132,4 +169,4 @@ Copy the URL from your browser to share your current cost query with team member
 [6]: /cloud_cost_management/saas_costs/
 [7]: /cloud_cost_management/datadog_costs/
 [8]: /monitors/types/cloud_cost/
-[9]: /cloud_cost_management/reporting/
+[9]: /cloud_cost_management/reporting/