Step1 : Create the Element and Element links
Step2: write the fast formula
Step3: Attach the fast formula in Formula Results

Package used to call the fast formula from the backed : ff_exec

Simple Code Snippet below: 

      l_formula_id        NUMBER;
      l_element_inputs    ff_exec.inputs_t;
      l_element_outputs   ff_exec.outputs_t;
      l_in_count          NUMBER;
      l_out_count         NUMBER;
      l_pay_value         NUMBER;

   BEGIN

      BEGIN
         SELECT formula_id
           INTO l_formula_id
           FROM ff_formulas_f
          WHERE formula_name = ‘XX_PAYROLL_FORMULA’
          AND p_effective_date BETWEEN effective_start_date  
             AND effective_end_date;
      EXCEPTION 
      WHEN OTHERS 
      THEN
      DBMS_OUTPUT.put_line (‘NO formula exists’);
      END;

      IF l_formula_id IS NOT NULL

      THEN

— Insert FND_SESSIONS row ( Optional )

  INSERT INTO fnd_sessions
             ( session_id, 
               effective_date
             )
        VALUES 
            ( USERENV (‘sessionid’), 
              p_effective_date
             );

—
— Initialize the formula.
—

ff_exec.init_formula (l_formula_id,
                      p_effective_date,
                      l_element_inputs,
                      l_element_outputs
                      );

—
— Loop through the Input Values
—
FOR l_in_count IN l_element_inputs.FIRST .. l_element_inputs.LAST
    LOOP

    —
    — Pass The each Input value name and its Value : Eg: START_DATE and p_start_date
    —    
       IF (l_element_inputs (l_in_count).NAME = ‘START_DATE’)
        THEN
           l_element_inputs (l_in_count).VALUE :=
                fnd_date.date_to_canonical (p_start_date);
        END IF;

END LOOP;

—
–Run The formula
—

ff_exec.run_formula (l_element_inputs, l_element_outputs);

—
— Get the Out Put Values
—
FOR l_out_count IN l_element_outputs.FIRST .. l_element_outputs.LAST

    LOOP
      —
      — Get all the Out Put Values Here L_PAY_VALUE is the out put value
      —
      IF (l_element_outputs (l_out_count).NAME = ‘L_PAY_VALUE’)
        THEN
           l_pay_value := l_element_outputs (l_out_count).VALUE;
      END IF;

    END LOOP;

RETURN (l_pay_value);

END;