No matter whether there is content or not, just like C language, a procedure SUB or a function FUNCTION must use parentheses, which is a fixed format.

It can be understood this way

If there are parameters inside, it means the input parameters

If it is empty, it means there are no input parameters, which means there are no parameters

private sub form_load() This represents the form loading event. It is a process and does not need to provide parameters, so it is empty.

private sub command_click(index as integer) This means that you have created an array of button controls. It means that there are many button controls with the same name. Then in the click event, you must tell the system which button you clicked. INDEX is the serial number of the control.