Formulas in HCM (taxes, vacations,....)

Hello Experts,

I would like to know where in SAP HCM do we enter/write the formulas used for calculating taxes, vacations, and different kinds of formulas ... (links on how to write formulas/ syntax an so is greatly appreciated)

(I can see the schemes in PE01,2,4 ... is that relative to writing formulas or what??)

thanks in advance