Cannot figure out how to get Account categories to add up
I probably laid out my 2013 expenditures poorly and I will do it differently with the new Numbers in 2014, however, I have a list of my expenditures one after the other by month and labelled as to whether it's gas, mortgage, etc. So right now my categories and chart show nothing other than my category listings and I do not know how to get Numbers to add each category up. Can someone advise me how to get for instance all my Gas expenditures from 12 months labeled as "Gas" to add up in the Account Categories as a total? Thanks.
imac, Mac OS X (10.6.7), Have two imacs