Move the mouse cursor to the position in the report where the result of the function should appear after selecting this menu option. Keep the mouse button pressed while adjusting the size of the function field. Once you release the mouse button, the function editor dialog will open, allowing you to enter the function definition.
Other options for the field can be modified via the [field properties](../../dialogs/field-properties/properties.md) dialog (floating menu) and the [format menu](../format-menu.md).