After installation of MySQL for Excel, startup Excel, go to the "Data" ribbon and on the right you should see a "MySQL for Excel" button. That should be the best (and preferred) way to connect to a MySQL database, using MySQL for Excel.
If you need to aggregate data from different tables, the best place to do that is in the database. Create a view there (MySQL has a Workbench that lets you do such things quite intuitively) and use that view as a basis for your Excel report. The advantage is that everyone now has access to that aggregated data. Also: databases are optimized to do things as aggregating data.