There is a full guide for visitor visas/supervisas on CIC website http://www.cic.gc.ca/english/visit/index.asp
You can also apply online http://www.cic.gc.ca/english/my_application/apply_online.asp You will need to pass online survey and based on the answers you gave, the system will show you the types of visa you (your parents) are eligible for. Documents checklist for your type of visa will be there too.
Yes, you can. Like i have said in one of the previous posts on this forum, technically if you applying on behalf of your parents, you need to mention it in the survey and the application itself. But most of the people don't do that. It will be easier if you help your parents to fill and upload the forms, as they do it themselves. The signature is digital anyway.