To use a predefined or custom function in your spreadsheet:

1. Double-tap on the cell where you want the result to be displayed.

2. Tap the = sign, then type the desired function's name. While typing, you can also choose from the function suggestions shown above the keypad.

3. In the function syntax that appears, enter the input values or choose the input cell ranges and tap ✓ to get the result.

4. You can also use the Insert > Function option to add a function.

5. To refresh the functions in your spreadsheet, you can use the Recalculate option under the Function menu.
   

6. ​You can also use the quick functions displayed on the top bar once a cell range containing numerical values is selected.