Auditor:

The auditor is the person hired by the owner for a systematic examination of books of accounts of the company. The auditor uses its professional knowledge and gathers evidence. It should be a question minded, plan, and being alert to the condition of the misstatement due to fraud and error. 

Manager:

A manager is a person hired by an owner to takes an important decision for an organization.

He minimizes or eliminates the error and safeguards and keeps control over the assets, expense, and inventory on the behalf of the owner. Internal control minimizes or eliminates the error.

Expense:

Expense is defined as the cost incurred to acquire something or in order to earn revenue; it is expired during the accounting period. It is an outflow of assets. So it is debited to the Income statement.

Example: Cash paid for salaries, rent, and depreciation.