Overdubbing   

After a first pass of recording one or more tracks it may be desireable to subsequently add more tracks. This is usually done by listening back to the original track(s), using headphones to minimize leakage, while recording the new one(s). This technique is known as overdubbing. 
 
Use the monitor section of the mixer to bring up the level of the prerecorded tracks to an appropriate headphone mix in order to hear these tracks while recording the new material. 
Bring the source signal to be recorded into the mixer and assign it to an unused track. 
Set the input trim controls to set levels for a nominal signal level to the mixer and use the faders to set the level going to the recorder. 
Bring up the appropriate channel on the monitor section of the mixer to be able to hear the new material with the prerecorded sound. 
Enable recording on the new tracks to be recorded making sure the rest are in safe mode. 
Start the recorder several seconds before the section to be recorded or from a musically useful point for the performer and start recording just before the signal to be recorded begins. Correcting mistakes or inserting material in prerecorded sections can be acheived by punching in.