Here is an example which is from Odoo 14 manufacturing documentation:  https://www.odoo.com/documentation/user/14.0/manufacturing/management/bill_configuration.html

For example here it's said: "Before creating your BoM, you have to create the product using the BoM and, at least, one of the components. Go to the Master Data menu ‣ Products and create both the finished product and the component."

Thanks. 

Hi,

You might be referring to a wrong documentation or an outdated documentation. Nice if you add the refereed documentation along with the question. 

Have a look at this odoo webinar about manufacturing:  Managing Custom Manufacturing/Job Shops in V14

Thanks