Well, I assumed you read the man page...
man diff
...otherwise, read...
http://unixhelp.ed.ac.uk/CGI/man-cgi?diff
For example:
File1
1col_1,1col_2,1col_3,1col_4,1col5
2col_1,2col_2,2col_3,2col_4,2col5
3col_1,3col_2,3col_3,3col_4,3col5
4col_1,4col_2,4col_3,4col_4,4col5
5col_1,5col_2,5col_3,5col_4,5col5
File2
1col_1,1col_2,1col_3,1col_4,1col5
2col_1,2col_2,2col_3,2col_4,2col5
0col_1,3col_2,3col_3,3col_4,3col5
4col_1,4col_2,4col_3,4col_4,4col5
5col_1,0col_2,5col_3,5col_4,5col5
diff File1 File2
3c3
< 3col_1,3col_2,3col_3,3col_4,3col5
---
> 0col_1,3col_2,3col_3,3col_4,3col5
5c5
< 5col_1,5col_2,5col_3,5col_4,5col5
---
> 5col_1,0col_2,5col_3,5col_4,5col5
...lines starting with "<" belong to the first file (File1).
lines starting with ">" belong to the second file (File2).
Is there somthing specific you are trying to do with diff?