Cordial means being poilite, while Brandy is a fine girl (what a good wife she would be, but my life, my love, and my lady is the sea, do do doo doo do do doo doo.)
There are many different kinds of cordials, brandy being just one. There are also Gran Marnier, drambuie, etc. Just check a dictionary for what the different bases are. Cordials are also called liquers.
Brandy is distilled from wine, and aged. It is NOT a cordial.
Cordials are sweetened and/or flavored liquors, usually with fruit. They are made from a base liquor, usually brandy or neutral spirits. They are also called liqueurs.