When you start working with Excel files, it is a good idea to understand the basic Excel file types and extensions.

A file is normally identified by a file name and a three letter file extension. Abstract.doc, for example, is a Microsoft Word document named Abstract. The three letter doc extension signifies that this file is a Microsoft Word document.

An Excel workbook identifier would have the form Filename.xls, where filename is the name of the workbook, and .xls is the extension signifying the workbook file type. When you want to open an Excel workbook, look for files ending in .xls

Another Excel file type is .xlt, signifying an Excel template file. A template files can save formatting, macros, formulas, and other customizations of an Excel worksheet.

If an Excel worksheet or work book is to be published as a web page, it can be converted to an .html or an .htm format. This extension signifies the hypertext mark-up language file type, commonly found on the World Wide Web.

Changes made to Excel toolbars are saved in an .xlb file so they can be retrieved when you open your workbook.

It is a good idea to keep your files organized by creating and naming appropriate folders to contain your files. You should also give your Excel files names that imply something about their content, like Budget03 or YearlyReport05.