TIme Management/ Payroll functions

Dears,

I am new to SAP HCM , i would like to know where exactly do we write the functions used to calculate/process the payroll and time data (like fast formula in Oracle ERP HR)

example:

if I want to put a rule for time events (clock in/ clock out) that applys when an employee comes 3 hours later than his work schedule. (something like that)

where do i write that formula

also where do i write formulas concerning taxes calculation in payroll (for example)

Note:

those calculation rules are not included in SAP as I am implementing the HCM for Egypt (which doesn't exist as a standard)

thanks in advance