A mixer will typically accept 3 inputs phono for turntables mic and line for everything else. Some digital mixers also have usb and firewire. You want 3 or 4 input channels because you never know you might have to use 2 turntables and 2 cd decks. If you get a cd deck make sure it is mp3 compatible. Anyway back to the mixer it will have cross fader and channels. When you are doing a set you want continuous music.