Show me how to perform mathematical operations on groups of cells in Microsoft Excel 2007

Excel -> Microsoft Excel 2007

Problem: I need to show the sum of all values in a column or row without manually adding all the numbers.

Open Microsoft Excel 2007
Select a group of cells that contain numerical values
On the "Home" tab, under the "Editing" section, click the "Sum" button (it has the sigma symbol on it - the sigma symbol looks like a Greek capital "E")
Right-click on the cell that contains the summed value
On the context menu, click the "Delete..." item
Select a group of cells that contain numerical values
Click the small down arrow next to the "Sum" button and choose another mathematical operation