The Companies section under the Contact Details page is for associations. If that contact record is associated to a Company Record, the company record will show up there and will be clickable which will direct you to the Company Details Popout.
Once on the company Details popout, the 'Contacts' section will then show any contact records that are associated to that company. The purpose of associations is that it will show other relevant outreach information i.e. if 3 contacts are associated to a company, you will see history from each of those contacts under the Company Details Popout.
The system auto-associates the People record creation based on email domain, for Example: if I have a company with the domain property uptics.io and import a contact [email protected], Spinell will be auto-associated to the Company. But you also have the ability to manually associate inside the popout. If you upload a separate list for your contact's companies, it would need the domain field filled out.
Per the example below, there needs to be an existing company record with the domain lavvoneacademy.com, and then there would be an association to the below contact record.