A View is basically only a SELECT
-statement. If you want to add another column to your view, just change the statement on which it is based. If you need a whole new column with new data, change the underlying table structure from which you are selecting the columns that are shown in your view.
For more information check the official Oracle documentation:
http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_8004.htm
Or see this question on SO:
What is a View in Oracle?