It lets you 'mix' your songs, by playing two or more tracks at the same time, adjust their relative speed so that their tempo will match, apply effects like loops etc, and crossfade from one side to the other. In the same way that the CD players used by DJs have more options than a regular Hi-Fi CD player, Virtual DJ for macOS has more options than a simple media player like iTunes. VirtualDJ for Mac is a software used by DJs to replace their turntables and CD players, and use digital music instead of vinyl and CDs.
