I'm actually on Odoo V9, and I'm trying to import a list of around 3000 customers to add it to my contacts. I actually want to import them with basic information, and adding their company at the same time. I got many different companies that are already writed on an excel file, but I actually really don't understand how the companies ID works.

When I'm trying to import, I always got an error if I put just a company name, that's normal I think, but actually, how to put a correct company ID ? I've created some company from contacts windows but I don't know which ID is linked with which company.