The access an employee has on the system is controlled by their security role. If their security role has 'Filtered by Logged in User' checked under CRM section, this will restrict employee to only see the customers/orders that they have been assigned.

If you would like your employee to see all orders/customers in the system, the 'Filter by Logged in User' box should NOT be checked.

For more information on security roles, see Settings - Security Roles.