In a list, above the list items, click Edit.
To the right of the column headings, click the Add button (the “+” sign).
On the menu that appears, click More Column Types.
In the Column Name text box, enter a name for the column.
Choose the type of information that the new column will store.
To work with columns, you must have Designer or Full Control permissions.
SharePoint includes several predefined columns. Instead of creating a new column, choose to add from existing site columns when editing list column settings.
In the Additional Column Settings dialog box, you can also optionally edit the following column settings:
Description . What you enter here displays under the field when the user is editing the form.
Require That This Column Contains Information . Select Yes to require data to be entered in this field.
Enforce Unique Values . Select Yes to require that each value in this column be unique in this list.
Maximum Number Of Characters . This determines the maximum number of characters that can be entered in this field.
Default Value . Any text entered here will be the default column entry when a new item is created.
Add To Default View . Select this check box to add this column to the default view of this list.
Column Validation . Use rules to accept or reject information entered in this column based on defined criteria.
Click OK.