Some information about using Miva is available in the online Help in the WebsiteOS. There are also many other sources of information.
Training Tools - Miva Merchant tutorial
http://www.trainingtools.com/online/mivamerchant/index.htm
Miva Corporation - Miva Merchant demo
http://www.miva.com/products/demo/Merchant/
Miva Merchant documentation for v2.22
http://www.miva.com/docs/merchant/mercdocs_222.pdf
Miva Merchant v2.22 release note
http://www.miva.com/docs/merchant/mm2.22_relnote.pdf
Miva Merchant HOWTO Guides including:
-Getting Started
-Making Changes to Your Store
-Setting Basic Miva Merchant Configuration
-Administer a Miva Merchant Store
http://www.miva.com/docs/merchant/howto.html
Miva Merchant v2.22 Installation Manual
http://www.miva.com/docs/merchant/mm2.22_install.pdf