With all new application there is a lerning curves.
I strongly suggest that you start by trying reproduce the samples provided in the tutorial video.
That will help you doing more sophisticated configuration like the one you require.
In you requirement, you want to move an existing website with its existing DB.
This is more complex and you must be more fluent with JMS before doing that.
You must understand how JMS is working that does not seems the case yet.
The fist element is to be able configure your hosting server with the subdomain and re-use the SAME directory path into JMS slave site deploy folder.
While you will not be able to do that correctly, this is a non sense to try explain you the more complex things that you have to do to move an existing website with its existing DB.
Concerning the blank page, this is frequently related to a PHP syntax error.
You can generally find the information into a file "error_log" present in the root or in the adminsitrator directory.
When you have the error, you need to read the source of the module, plugin, component that generate the error to understand why.
See our previous reply to the advised on the structure
www.jms2win.com/forum/24-joomla-multi-si...lt-to-configure#3796