just unzip in into joomla base dir
go to joomla admin, then to virtuemart admin
section Stores
add payment module
choose 
Payment method type: HTML-Form based (e.g. PayPal)
Payment class name: ps_gspay
Enter all other option as you like
press 'Save' button

then go to the 'list payment modules' section
choose your new gspay module, click preferences
enter your SiteID asigned by GSPAY system (NOT merchantID)
save

now you can use gspay payment in virtuemart.


