Oral things have to do with the mouth. For example, oral surgery involves surgery done in the mouth, and oral arguments are ones made by mouth (i.e., spoken instead of written).
Aural has two main definitions: (1) of or relating to the ear and hearing, and (2) of or relating to the aura. As the noun aura is loosely defined and is mainly confined to a few esoteric subjects, the first sense is the more common one. Aural in this sense is synonymous with auditory.