How do Voices Work?

Can someone give me a primer on how voices work? I’m having a lot of difficulty predicting stem order and figuring out how to come back to a project and know how many times to hit Shift-V to get “the blue one” I was working on. (And is there a difference between 3-up and 3-down? Is that just two ways of entering voice three or are they treated as separate voices?)

I also can’t figure out how to select a group of notes from a voice and delete/transpose/change stem direction on them without selecting everything else in the process (like in Sibelius’ select filters.)

Or is this one of those “later update” things that means this is yet another project I have to put on hold until March?

Also…here’s a picture of a score I was working on. Everything was fine until I saved it and came back later and was completely unable to continue the same voices (colors) in m. 9 no matter what combination of Shift-V or starting this or that part first I tried:
Screen Shot 2016-12-20 at 5.31.26 PM.png
I don’t even know which voice is which at this point. :frowning:

I think the basic problem is that you’re always using Shift+V when when you want to switch to another voice. You only need to use Shift+V the very first time you want to start a new voice: after that, you need only use V on its own (without Shift) to swap the caret between the voices you’ve already created.