The user manual is actually in the system itself; each module has its own user guide. Please follow the steps I've included below to get them.
Go to the Payroll module, click Help, and select Content.
Go to the Core module, click Help, and select Content.
Go to the Leave module, click Help, and select Content.
Go to the Costing module, click Help, and select Content.
Go to the HR module, click Help, and select Content.