The differences between these 3 types of blots are described in your textbook.
In a Southern blot, DNA restriction fragments are separated by gel electrophoresis,
transferred to a membrane, and probed by hybridization with a specific cloned
nucleic acid probe. A Northern blot is similar except that RNA molecules
are separated by gel electrophoresis and transferred to a membrane. In the
case of Western blots, protein molecules are separated by gel electrophoresis,
transferred to a membrane, and probed with specific antibodies. Note that
nucleic acids cannot hybridize with proteins.