Please some one help me on compare two work sheet cell by cell

One way is to use a third sheet, put this in A1
=IF(EXACT(Sheet1!A1,Sheet2!A1),"y","n")
then copy A1 and paste it into the rest of the new sheet, as far as needed.

Since EXACT is case-sensitive, "this" is considered different from "This".

Don't be tempted into using the comparison Sheet1!A1=Sheet2!A1 because it considers 0 and FALSE and an empty cell to be all the same.

A different way is to use conditional formatting to color the cells of Sheet1 that are different from their Sheet2 conterparts. This way, there's no need for a third sheet. Look in Excel's built-in Help to read about conditional formatting.