Relationships link Contacts and Accounts. The relationship tab in the Accounts or Contacts section displays the current relationships tied to that account or contact; the relationship tab in the Accounts section also allows you add relationships. Each account can have one or more contact relationships, and each contact can have one or more account relationships.
Relationship Types are specifically used to categorize the Contacts who are tied to the Account or vice versa.
To give editing/viewing privileges of an Account to a Contact, assign Account Ownership by clicking the checkbox next to the Contact name.