The data set is not a file, it is a folder which contains other folders and files. The naming convention is yourdatasetname.moneydance. The default location for a data set can be found by clicking on HELP – SHOW DOCUMENT FOLDER in Moneydance. This should open your file finder. If you won’t to move your data set, close Moneydance and move your data set to the new location. Open Moneydance which should open in the Welcome to Moneydance window. Click on “Open others” and navigate to your data set in it new location and click on your data set folder. Moneydance will remember this new location.
Moneydance has an inbuilt sync engine which allows you to work on the same data set on two computers at different or even at the same time. You have a number of options to do this the best and most flexible is called “Dropbox Folder”. See http://help.infinitekind.com/kb/syncing-and-sharing-data You will need to download and install the free version of the cloud sharing client from Dropbox.
I also use Dropbox as my backup location in case my local hard drive fails. Moneydance has an automatic daily backup and a manual backup “Export Backup” which you can perform at any time.