The AND function is another of Excel's Logical Functions. In general, a logical function only gives you a true or false answer. It evaluates the data in a spreadsheet to see if it meets the specified criteria. If it does, the function returns a True response in the cell where the function is located. If not, a False statement is returned.
In Excel 2007 the AND function allows you to specify up to 255 criteria to be evaluated. All of these criteria would need to meet the specified criteria for the function to give you a True response.
In Excel, the AND function is often combined with other functions, such as the IF function to greatly increase the capabilities of your spreadsheet.
To find out the details on using this function, read this short tutorial on the Excel AND Function.