The task is descrived on ENS product guide, P.48 [Common -Tasks].
I think we can creat the "Task" on ePO side, my understanding is correct?
The guide you linked is for the Endpoint Security Client Interface, which refers specifically to the GUI Client on the endpoint. The tasks it's referring to in that guide are mirrors, client updates, quick scans, and full scans. These can be configured in ePO under:
1) Default Client Update Task: Endpoint Security Common : Policy Category > Options > Your Policy
2) Quick/Full Scans: Endpoint Security Threat Prevention : Policy Category > On-Demand Scan > Your Policy
For Quick/Full scans, to actually apply them to a set of systems, you can assign them to a group, under Assigned Client Tasks: