Whether you type 8/22/2010, 22-Aug-2010, or even August 22, 2010, it's all stored as serial number 40412. Sometimes, Excel might surprise you by changing the date from the format you typed it in to its default format. But regardless of the format, the date's serial number is 40412.
The exception is if you use a format that Excel doesn't recognize as a date. For example, if you typed August-22,2010 or 8,22,10, Excel would store that information as plain text, not a serial number.
To change the format — or see some of the other ways you can use slashes or hyphens to format dates — open the Format Cells dialog box shown in the picture by right-clicking on a cell with a date in it and choosing Format Cells. Alternatively, you can jump right into the practice, where you'll see and try out the process for yourself.