The key to managing your account successfully is accurate categorization of your transactions. There are a number of ways to categorize and verify that your transactions are correctly categorized.
First, you need to do your categorizations through the Transactions page. You can categorize individual transactions by clicking on and expanding a transaction, then selecting the proper category or sub-category from the Category dropdown menu.
You can also select multiple transactions to categorize the same way by checking off the boxes on the left of the transactions, and again selecting the proper category or sub-category from the highlighted dropdown menu at the top of the transactions list.
You can create your own sub-categories by clicking the Settings gear at the top of the header and select 'Categories' from the drop list.