In the Core eDiscovery (Microsoft Purview) workflow, you first create a case, add case members, and then (typically) apply eDiscovery holds to relevant locations to preserve potentially responsive content before you run searches. While a hold isn't strictly required to execute a search, Microsoft's documented workflow shows holds occur prior to creating and running content searches so that items aren't altered or deleted during the investigation. After holds, you create searches, review, and export.