Step 1:
Create a sync group and a cloud endpoint
A sync group defines the sync topology for a set of files. Endpoints within a sync group are kept in sync with each other. A sync group must contain one cloud endpoint, which represents an Azure file share and one or more server endpoints. A server endpoint represents a path on a registered server. A server can have server endpoints in multiple sync groups. You can create as many sync groups as you need to appropriately describe your desired sync topology.
A cloud endpoint is a pointer to an Azure file share.
To create a sync group, in the Azure portal, go to your Storage Sync Service, and then select + Sync group:

In the pane that opens, enter the following information to create a sync group with a cloud endpoint:
Sync group name: The name of the sync group to be created. This name must be unique within the Storage Sync Service, but can be any name that is logical for you.
Subscription: The subscription where you deployed the Storage Sync Service in Deploy the Storage Sync Service.
Storage account: If you select Select storage account, another pane appears in which you can select the storage account that has the Azure file share that you want to sync with.
Azure file share: The name of the Azure file share with which you want to sync Enter: share1 Step 2:
Create a server endpoint
A server endpoint represents a specific location on a registered server, such as a folder on a server volume.
To add a server endpoint, go to the newly created sync group. Under Server endpoints, select
+Add server endpoint. The Add server endpoint blade opens. Enter the following information to create a server endpoint:

Registered server: The name of the server or cluster where you want to create the server endpoint.
Enter: SRV1
Path: The path on the Windows Server to be synced to the Azure file share. The path can be a folder (for example, D:\Data), volume root (for example, D:\), or volume mount point (for example, D:\Mount).
Enter: C\app
Step 3:
Create an Azure File Sync server endpoint
To add a server endpoint, go to the newly created sync group. Under Server endpoints, select
+Add server endpoint. The Add server endpoint blade opens. Enter the following information to create a server endpoint:

* Registered server: The name of the server or cluster where you want to create the server endpoint.
Enter: SRV1
* Path: The path on the Windows Server to be synced to the Azure file share. The path can be a folder (for example, D:\Data), volume root (for example, D:\), or volume mount point (for example, D:\Mount).
Enter: C:\app
Step 4:
To add the server endpoint, select Create. Your files are now kept in sync across your Azure file share and Windows Server.
Reference:
https://learn.microsoft.com/en-us/azure/storage/file-sync/file-sync-deployment-guide
https://learn.microsoft.com/en-us/azure/storage/file-sync/file-sync-server-endpoint-create