GST General guide
http://gst.customs.gov.my/en/rg/SiteAssets/general_guides/Revised/General%20Guide%20-revised%20as%20at%2027%20October%202013.pdf

GST double entry
(Refer to attachment "Accounting & Software Entries"

Tax Invoices and Simplified tax invoice
http://gst.customs.gov.my/en/ib/Pages/ib_iti.aspx

Credit Note or Debit Note