Double Entry basically refers to the DUAL ASPECT of a single entry , namely DEBIT & CREDIT. Any entry that we do, has a Debit side and a Credit side..
The practice of double entry has its foundations based on the three basic principles of Accounting, which are:-
1. In case of Real Accounts, Debit what comes in, Credit what goes out.
2. In case of Nominal Accounts, Debit the Expenses/Losses, Credit all Receipts/Incomes.
3. In case of Personal Accounts, Debit the Receiver, Credit the Giver.
By fully understanding these three basic principles of accounting, one can successfully understand and implement Double Entry Accounting.
For eg.,
1. Purchase of goods will be entered as, “Debit Purchases A/C & Credit the name of party from whom we have purchased goods.”
2.  Payment for the goods purchased will be entered as, ” Debit the name of the party & Credit Cash/Bank A/C”