Companies sit under a Company where Contacts can be created and Sales Ledgers can be set.

From a Company, you're able to view all Contacts, Opportunities, Problems, Quotes etc. which sit under the Company.  

Selecting one of the pages on the left-hand side will show any records created at any level of the hierarchy under the Company.

Additional records can be created from a Company and this is done by selecting the plus icon on the right-hand side.