MS Excel files are called Workbooks. One page of a workbook is called a Worksheet. One square in a worksheet is called a Cell .

On main use of Excel is for performing what-if analysis.  Basically this means changing the numbers in some cells, and seeing how the numbers in some other cells change. The numbers in the other cells change because they are based on a formula that depends on the cells that were changed.

The Excel package is similar in function to any other spreadsheet package.  One aspect in which the Excel Worksheet is different is that it can hold not only data and formulas, but also graphic objects like pictures and images. 

Excel also allow you to define macros , which you can use to combine a series of actions to automate your work. 

You can also use Excel for information storage. You can set up a group of cells as a database.  You can find, update and add information.  You can extract information that matches any criteria that you specify.