880ex overdubbs??

[GrahamCA]

. I am using an 880ex version 2.004. I am trying to put a song together. I have :
beat - trk 1
vocal - trk 2
overdub - trk 3
overdub - trk 4?????? hopefully
I dont know how I got trk 3 to overdub. I read the manual and fooled around a bit and got it to work but now I cant get other overdubs to record to trks 4,5,6.
Could You give me a simple way to overdub my vocals or add more parts to the song. The start up guide sucks. Any help would be great. Also I have a plextor 4220 burner. When the screen says 7-1 8-1. Where do I assign these for when I burn my cd? I have been putting them on 1-1 , 2-1 and I am only getting sound out of the left speaker. I am totally confused with this unit. All I want to do is record a beat on a trk , then a vocal on trk 2, overdub on trk 3, adlib on trk 4. The manual doesnt really help me out. Please help meeee.
Thank You,
Graham