Hi,
1. You need to go in the Joomla plugins manager and search for the HikaShop google products plugin. Edit it and configure it accordingly to its tooltips. You'll have to trigger link at the bottom of the settings to get a XML file you can import into google merchant.
2. Yes, you can just click on the "export" button of the products listing to get a CSV file of all your product data. I'm not sure why it wouldn't do anything when you click on it. You should at least get an error message normally if it doesn't work.
In most cases however, it doesn't work because there are too many products and not enough memory available to load them all from the database and thus it requires increasing the memory_limit of your php.ini. But since you don't get the error message it might be something else.