How to add new fields to standard alv report

Hi,

Tcode(VL10G) .ie.out put list will not showing one new field.I want to add one more field to output list. append the field(VIKP-SDABW) In the SHP_VL10_ITEM structure .And write the logic in the exit LV50R_VIEWG05----

>USEREXIT_PREPARE_LAYOUT_FILL.Please expain what is the process?

Why i have write the code?what logic i will write?

Thanks & Regards,

sairam