Scroll down or click here for an introduction to Excel. Click on the menus on the image below to find out about Excel's menu commands.
These screenshots are from Excel 97, part of Office 97 for Windows. However, the extensive information provided about the various menu options is almost entirely valid for all versions of Excel, from version 95 to the current version. Most changes to Excel since 1995 have been cosmetic, and do not affect the accuracy of the information provided here when applied toward different versions.
[File Menu | Edit | View | Insert | Format | Tools | Data | Window | Help Menu | Page Setup]
Excel is used to organize, calculate and analyze business and scientific data. It can be used to create budgets and invoices, to process large quantities of data... Excel handles repetitious tasks and outputs results numerically and graphically.
Excel
documents were originally limited to one page.
These documents were called Worksheets. After the first few versions of
Excel, Microsoft introduced the concept of Workbooks, which contain
multiple Worksheets. The Worksheets in an Excel Workbook are accessed
by clicking on the tabs at the bottom of the Workbook window:
Each worksheet
organizes data in cells, rows and columns. Columns and rows can be resized
by clicking and dragging on the divisions between the row 
or column 
headings. Rows go across the page and columns go up and down the page.
Row headings are denoted by numbers (1, 2, 3, ...) and column headings
are denoted by letters (A, B, C, ...). Double-clicking with the resize
tool ()
will AutoFit the column to fit the size of the cell with the largest contents
(try typing Wednesday into a cell and AutoFitting it). Note
that newer versions of Excel may AutoFit for you as you enter the cell
contents.
Cells are denoted by the column and row where they located. Cell E3 would be the fifth cell across and the third cell down. You refer to a range of cells when you want to perform an operation on them, for example to calculate their sum. A range of cells is denoted by the first cell (upper left) and the last cell of the range (lower right), separated by a colon. For example, A1:C18 denotes all cells from column A, row 1 through column C, row 18.
The cursor
in Excel changes from an arrow 
to a "plus" 
when it is placed over cells. The "plus" is called the cell
selection tool, and can be used to select a single cell by clicking
on it, and a row or column by clicking on the heading. You can select
contiguous groups of cells by clicking on one cell in a corner of the
group and dragging the cell selection tool to the opposite diagonal corner
of the group.
If you can open
Excel now,
try selecting cell ranges, rows, and columns .
Resize rows
and resize columns .
A cell does not always display what you have entered into it. If you enter a formula into a cell, then the cell will display the results of that equation. While the result will be displayed in the cell, the formula will be displayed in the formula bar when the cell is selected. The formula bar is located below the toolbars, above the Worksheet window, and the selected (active) cell is listed to its left (see above).
Click on the menus
on the image above to find out what they do.