The Index Function:
The INDEX function in Excel is fantastically flexible and powerful, and you’ll find it in a huge number of Excel formulas, especially advanced formulas. But what does INDEX actually do? In a nutshell, INDEX retrieves the value at a given location in a range. You can use INDEX like this:
=INDEX(B3:B11,4)
To summarize, INDEX gets a value at a given location in a range of cells based on numeric position. When the range is one-dimensional, you only need to supply a row number. When the range is two-dimensional, you’ll need to supply both the row and column number.