Payroll preparation user guide

Hello,
I have some troubles with payroll preparation module. In fact, I don’t really understand how to create expense, bonus, lunch voucher and add them into payroll preparation of 1 employee.
Do you have any detail user guide of this module or the HR flow document? It’ll help me and my project a lot during study Axelor
Many thanks,

did you check here : https://www.axelor.com/functional-documentation ?