Understanding accounting

Hi Champs,

I need help in understanding accounting though it is very basic.

How debit and credit applies to Profit and Loss Account.When we debit and credit Profit and Loss account.

Below is a piece of text i got from other website

• Assets and Expenses
  An increase is recorded as debit (left side)
  A decrease is recorded as credit (right side)
• Liabilities, Equities and Revenues
  A decrease is recorded as debit (left side)
  An increase is recorded as credit (right side)
• Contra-accounts
  Contra-accounts behave exactly in opposite way to the respective normal accounts.
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• Why is it all ways we need to follow above rules any reason behind above statements.
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• Any good book or websource for understanding financial accounting.
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