Regards

Hi,

you can refer to this link: 

https://www.youtube.com/watch?v=rZaHSTvljuA

https://www.cybrosys.com/blog/how-to-create-and-configure-sub-modules-on-the-odoo-sh

Hope it helps

Hello,

Yes, if you want to customize or add new functionality then you have to use odoo.sh or on-premise.
In odoo online, you can make limited customization with the help of odoo studio.

Thanks,
info@creyox.com