Flip the D3200's power supply switch to "On," and press the "On" button at the top of the unit. Press the "Rec/Play" button, located above the D3200's channel row.
Press the "Channel" buttons above all of channels you wish to record and dub. Pressing the "Channel" button toggles the associated track channel between playback, recording and inactive mode. A red LED indicates that the track is set for recording. A green light indicates that the track is ready to play back audio. Toggle the channel light off, which means that the track will be inactive.
Press the "Rec" button, then click "Play" to begin recording your audio. Press the "Stop" button after you've completed your recording.
Play back your overdub. Set all active channels to playback mode -- press their channel buttons to toggle their LED lights to "Green" for playback. Press "Play" to play back your overdubbed recording.