The Excel Indirect function converts a text string and into a cell reference.
If you type the reference B1 in an Excel formula, Excel understands that this refers to cell B1. However, Excel does not understand the text string "B1" to be a reference. Therefore, if your cell reference takes the form of a text string, you will need to use the Indirect function to convert this into a reference.
The format of the Indirect function is :
where the arguments are as follows:
ref_text    The text describing the reference 
a1   
An optional logical argument that defines the style of the ref_text reference.

By default, Excel uses the A1 referencing style. If you want to use the R1C1 referencing style, you will need to set this in your Excel options. To learn more about referencing styles, see the Excel Reference Styles page.
The following spreadsheets show simple examples of the Excel Indirect function.
Formulas:

Results:

Note that, in the above examples :
If you get an error from the Indirect function, this is likely to be the #REF! error:
#REF!    Occurs if the supplied ref_text cannot be interpreted as a valid cell reference. 