How add a new email template on behalf of exicisting one?

It might be easier just to change the existing template to what you want it to contain rather than creating  a new one but if you want a new template then i would remove the Screen from this tempate and then change where this template is being called for example on the Mailing & Printing tab on the Vendor or Vendor Class

Also other place it could be set it on the Purchase Order form itself 

Hi,

I need to know that how the system activate these email templates. Is there any check box to activate each templates or when we create new templates, it will be automatically activated. 

Thank you.

Not sure what you mean by Activate the template once the template is created then it can be used? The template is only used automatically if the form or Vendor is told to use it when emailing the form or you select it from the list to use.

Hi,

Thank you for your prompt attention regarding my matter.

Thank you.