Hello Joesi, 
Sellacious dashboard is the only way to add a product in sellacious. if you are referring frontend as 
https://www.xyz.com it is still under consideration whether to support it or not. 
As creating product require lot of information to be filled thus seller will login into 
https://www.xyz.com/dashboard (where dashboard is sellacious dashboard) seller will see the only information he is meant to see, you can control it from permissions (
https://www.xyz.com/dashboard login as admin and in left menu under settings you will find permissions) 
Let us know if that works for you. I am always available on skype and whatsapp if you need any further support. 
-Regards
Abhishek