The project copy button just copies the project source details to target side - handy when you are comparing two DBs on the same server.
You need to run the structure compare first (loads the schema and discovers which tables can be used in a data compare). So setup the project with source and target details and then click compare.
Then once the structure compare is complete click the data tab and the Wizard button to define to data compare setup. Then run the data compare.
Hope this helps.