The AutoSum feature in Excel provides a shortcut to adding up columns or rows of numbers in an Excel spreadsheet. It can add up to 255 numbers at one time.
Using the AutoSum feature in Excel is fairly simple, according to About.com Spreadsheets. After the numbers to be added are entered into either columns or rows, simply highlight the rows or columns to be added, then click the AutoSum button. Excel then adds all the highlighted numbers, depositing the answer in the next cell in the highlighted column or row. The complete function appears in the formula bar above the spreadsheet.