Copy Routines.....

Hello Experts,

I have created an extra tab in VL01N which contains 6 fields. the same tab i have also created in VF01.

now when user enters data in VL01N data should get copied while creating invoice..

I have searched SDN, Googled about it.

i found that i have to implement a routine.. I have never worked on routine before.

So please can anybody help me with how to create a custom routine. i dont want the steps, i want what pre-requisite i need for writing custom routines, how can i write the code? i have gone through some standard routines for eg LV60A003.

But i did not get anything from that. so please can anyone help.

Is there any other way than writing routine for implementing above scenario.

Thanks,

Amar