Like DaveO, I have a 414 but it has been a while since I used it. So: On machines like the 414, some of the controls do duoble duty. For instance, when you are recording, you use the pan switch to "assign" what you are recording to a particular track. AS mentioned in other posts, track 1&3 are "left", and tracks 2&4 are right. The best example is when you're doing an overdub. You plug your mic or (other input device) into channel input 1. You then set the switch to L, and pan all the way L, and all of the signal you're sending into the unit goes to track 1.
If you then want to add another track, you can leave everything plugged into channel 1, but you now set channel 2 to R and pan all the way to the R. Then when you record the second track, it all goes to track 2, without any of the signal being recorded onto the track you already laid down on track 1.
That is what it means to "assign" a track. You could plug your mic into the input on channel 4, set swithces on channel 1 to record, L, and pan all the way to the L, and even though you're plugged into the channel on the far right you are recording on the track on the far left. Once you get the hang of it, it all makes sense... or even if it doesn't make sense, it works!
"Using your Portastudio" is a helpful book. I also got a lot out of "The Billboard Guide to Home Recording", which is maybe kind of a dinosaur, but very helpful about machines like the 414.