Why is this so difficult to find??? How do I add/edit an Expense Category?

Let me help you find it, Create a journal entry.

You can add or create an expense category by recording it using a Cheque or Expense. They both report a transaction as an expense and a payment at the same time.

If you're referring to categorising a downloaded transaction to expense, though, I'll walk you through the steps:

1. Click Banking, then go to the Banking tab.
2. Go to the For review tab.
3. Select the transaction, then click the Categorise radio button.
4. Under Category, select an expense account.
5. Click Add or Match.

For more information, you can also check this article: Categorise and match online bank transactions in QuickBooks Online.

Feel free to get back to this thread if you have more questions. We'll reply to you as soon as we can.