On the Payroll Assignments select the "EmployeeID" that will start during the year. Then using the "Specify Payroll FTE Allocations" enter in their OrgUnit and ActNum and the portion of FTE time the employee will start work in the appropriate month.
To review how this employee is being budget click on the
magnify glass and the "Payroll Projection Preview" screen will appear with budget information for the selected employee.