To create a custom number format, select a cell that contains a number you want to format and invoke the Format Cells dialogue box. You can do this by right clicking on the cell and choosing Format Cells from the drop down menu or by choosing Format->Cells from the menu bar. When you see the dialogue box, click the number tab.

You can see the number you are formatting in the Sample area of the box.

To create a custom format, You must select custom from the bottom of the category list at the left of the dialogue box.

Once you click on Custom, you will see a text window containing a list of symbolic formatting codes underneath  the heading Type:

If you click on a symbolic formatting code, you will see what your number will look like with this formatting applied to it in the sample area above the formatting code list.

Try clicking on different format codes until you find one that formats your number close to the way you want it.

Let’s say that you want to format your number so there are two places after the decimal, and a dollar sign at the right side of the number.

To achieve this, click on the #, ##0.00 format code from the list, and look at your number in the sample field. Now add a $ directly to the right side of the format code where it is displayed directly beneath the Type: heading.

Click ok to format the cell or range of cells with this new custom format.

Here is the new custom number format applied to the cell.

The format code for your custom number format will be saved at the bottom of the format code list in the Format cells dialogue box.

To apply a custom date format, first select a cell or range of cells to apply the format to.

Next, invoke the Format Cells dialogue box by selecting  Format->Cells from the menu bar, and click the Number tab. Select Custom from the category list and the dialogue box should look something like this.

Enter the custom format code ddd/mmm/yy into the text field directly beneath the Type: heading. The ddd signifies a three letter abbreviation for the day, and the mmm signifies a three letter abbreviation for the month.

The Dialogue box should now look like the one shown here.

To apply this formatting to the selected cells, click the OK button.