When you need to pick a value from a list of values depending on an index number, choose function is the one you need.
Choose function selects from values specified depending on an index number. Below formula will result as value for index_num=1, value3 for index_num3).
For an example, lets say you have a number for month in a list of sales in columns A to D. You want to display full name of that month instead of month number.
To do that make a list of 12 months from January to December in column F (from F2 to F13) and name it months. Than name column as months. Now in D2 type following choose function:
When you hit enter, you will get corresponding month name for month vaule in column C.