Hope you can help me.

I have data from two months.
June & July.

I have already reported June's and don't want to report the same data in
July.

How can I extract only the "new" information?

Data1 Data2
a a
b c
d d
e e
f g
h h

The new spreadsheet (column, whatever) would yield:

Data3
b
c
f
g