That's easy. The $200 would be income (that had no associated expense!) So, you credit your income account (income generally reflects your effort "going out"

That's easy. The $200 would be income (that had no associated expense!) So, you credit your income account (income generally reflects your effort "going out" - did you have to make someone like you to get a gift?) And you debit your cash account $200. Everything is balanced. At the end of the year, you close your books by debiting income and crediting owner's equity. That's you. Congratulations! (See my post on debit/credit above).