Okay, as you said, I have to create a simple Select query first, then it lets me in the Query Builder. Only strange thing that I see now is that the joins I have made in the Model Database were not kept. Also, if I make the joins again in this Query Builder window I lose the arrows in design view mode (to give it a name to the query builder window) but I keep those joins in the SQL Statement tab below. Strange. Not the best way to work, I see everything goes well on the tutorials, maybe I'm doing something wrong? Also, if I save the PHP page where I was creating the MySQLi recordset and re open it, the recordset is not saved.
P/S: see screenshot please.