how to use the Integration Service Environment in Azure ?

 we can access to Vnet from Azure Logic Apps by using Integration service environments ( ISEs ).

( scenario, when to use it , sometimes your logic apps and integration accounts need access to secured resources , such as virtual machines ( VMs ) and other systems or services, that are inside an Azure virtual network.

To setup this access, you can create an ISE , where you can run your logic apps and create your integration accounts.

reference 

https://docs.microsoft.com/en-us/azure/logic-apps/connect-virtual-network-vnet-isolated-environment-overview