What type of accounting standards do managers utilize?

Can anyone assist me in understanding which accounting standard (IFRS or GAAP) managers utilize?

The question is irrelevant. Accounting standards prescribe how you must use your accounting knowledge and tools. Manager is just a tool that can be used no matter what standards you follow.

Manager basically adheres to two fundamental accounting principles:

  1. In every transaction, debits must equal credits.
  2. Assets = Liabilities +Equity