After you have set up the appropriate SLA Domain, you then map a virtual disk to that SLA Domain, which will schedule snapshot creation for the virtual disk, based on the periodicity and retention of the mapped SLA Domain.
Select the virtual disk from the Virtual Disk Management tab, click on the ellipsis (...), and select Snapshots.
In the Snapshots of <your virtual disk name>, select Schedule Snapshots.
Choose the desired SLA Domain, and select Save. Snapshots will now be scheduled and will be deleted after the retention period.