PA40 txn: This is for any personnel action that has been configured under SPRO-> ... Personnel Admin...>Personnel actions (T529A). The list of such actions depends on the user group dependence and the log on user's user group. Examples: Hire an employee, Transfer employee, etc.
Here also there nay be an action to terminate an employee,
PC00_M40_TERM txn: This Termination Workbench txn is linked to the program that processes termination. You can enter personnel number/s, Then select one pernr, double click it to go to next screen; then enter separation date (last day in service), separation reason (eg, resignation, terminated, etc, depending on config). Each reason is linked to a separation model. Then you can calculate pay for the employee. This will simulate the payroll to calculate all payments till the last day in service; this may include leave cash out, any separation pay (like x weeks for each year in service, etc). These payments depend again on the config. You will have payment rules configured and linked to the separation model.
You can complete termination - which processes the same action group for termination as in PA40. Group certificate can be printed.
Under your molga's payroll in IMG, there is a node for termination. All the steps under that need to be configured, before you can use this txn..
For more info, review your payroll guide, see the SAP Help Portal or google where you can find lot of info (including from SCN).