Help me add error bars to my Excel charts

Hi,I am posting this here since I thought there would be someone who may know how to do this. I am trying to add error bars to a bar chart in Excel. The Help instructions say 'select the data series and then on the Format menu click selected data series'. When I do go to the format menu to select the data series, there isn't that option. What am I doing wrong? It's my first time to try this, please help