When I have to compare data between 2 sheets, I use the Vlookup function and return a value from the 2nd sheet if a value from the first matches one on the 2nd...
If the first cell you are wanting to bring back a match is A1, go to the first blank column to the right.
go to the functions and chose Vlookup
your lookup_value will be the column you want to see if there is a match on sheet 2 (column A) A:A
tab to Table_array
Your table_array will be what column you want to look for the match on the other sheet...if you are looking in column B, highlight column B and C (or whatever value you wish to return upon a match)
tab to col_index_num
If you want to return value from column C you would count your columns from B to C which would be 2 so put 2 here.
tab and type in false.
Hit ok..
go back to sheet 1 and drag or copy this formula down the length of your data. Everytime there is a match on sheet 2 for the values on sheet 1, a value (from column C in this example) cooresponding to that match will be returned.
Not sure if this will help or if I explained it well enough but I have found it a very useful tool when comparing sheets with one another.
Keden