In the upper right-hand corner of your profile, you will find a money-bag icon - a financial summary of your transactions. Here you will see what you have sold, what items you have bought, and which of your posts have not sold.
Additionally, all the items you sold are visible in your profile. To search for them more easily, select the Sold filter.
A place where you can not only keep track of your financial transactions but also see exactly how much money you currently have is the Wallet.