Run Reports by Category

Morning All

I would like to try and run a report by category and I seem to be struggling.  I have been into the customization area but not really sure what I should change it to?  I have recently added 7 months worth of invoices to Quickbooks and I am concerned that due to the volume I may well have put a few invoices into the wrong category.  I have already found the gas bill in payroll, so I want to make sure I have coded everything correctly before it goes to my accountant.  Thanks very much