In double-entry accounting, rather than using a single column for each account and entering some numbers as positive and others as negative, we use two columns for each account and enter only positive numbers. Entries in the left column are referred as debits, and entries in the right column are referred to as credits.
Two accounts always are affected by each transaction, and one of those entries must be a debit and the other must be a credit of equal amount. Actually, more than two accounts can be used if the transaction is spread among them, just as long as the sum of debits for the transaction equals the sum of credits for it.
Whether a debit or a credit increases or decreases an account balance depends on the type of account. Asset and expense accounts are increased on the debit side, and liability, equity, and revenue accounts are increased on the credit side.
Review some examples of how income, obligations and payments are handled in double-entry accounting.