Last try. You're mixing pieces of two concepts together that really should be kept separate. Income statement and balance sheet.
Income statement is where you track net income (revenue less expenses). This will show you where cash is coming from and where it's going. So if you buy $200 in books this month, you have a $200 expense. If you sell $50 in books, you have $50 in Revenue. End of the month you have a net loss of $150.
But, you still have (in theory) at least $200 in assets ($50 cash and $150 or more* in inventory). This is balance sheet. Assets (what you have or what is owed to you) minus liabilities (what you owe, such as a loan or credit card balance) = equity.
*If, for example the $50 in sales were from books that cost you $10, your balance sheet would look pretty good because you would have assets of $240 even though you operated at a loss that month. Why? Because you started with $200 in inventory, generated $50 in revenue, but only depleted your inventory by $10. $200+$50-$10= $240.
This is a very simplistic method of bookkeeping, but I hope it helps to at least show you that you're not as in the red as you may think.