With Microsoft Fabric Lakehouses you begin with a starter pool for Spark. Patrick shows how you can create custom pools and have those as the default for your workspace.
Configuring starter pools in Microsoft Fabric
https://learn.microsoft.com/fabric/data-engineering/configure-starter-pools
How to create custom Spark pools in Microsoft Fabric
https://learn.microsoft.com/fabric/data-engineering/create-custom-spark-pools