Need to get selected grid records in one form and sum the amount field of selected records and pass the total amount into another form

Hi Everyone,

                      I'm the beginer in AX.and i'm facing the issue regarding a customization..I need to select the records in one form and sum the amount or quatity field of that selected records and have to pass the sum or total amount of that to another form...which is a menubutton in that main form...

Thanks in advance...