I am literally a newbie to this but I have searched online and in the forums and cannot find a solution to this super basic problem. Any guidance to my ineptitude would be greatly appreciated.
I am trying to line up two tracks so one starts where the other one ends and make it one track. My problem is I cannot get both .aup tracks to open in one screen. They open in a separate screen that I cannot see unless I minimize the current screen. So I can never splice these two tracks together as they are never on the same screen for me to do it. Is my mistake that they need to be converted to wav or mp3 files first? Does audacity not allow .aup audio file tracks to be merged? I have the latest download for audacity but these tracks were made before that.
This is driving me batty 
So “copy” the track on your second screen, by pressing Ctrl+A, then Ctrl+C. Now navigate back to the first screen and click at the very end of your track. Then press Ctrl+V. Presto!
I will try that again. It won’t paste after I’ve copied it, but I will try using Ctrl commands instead. Thanks 
If for some reason it won’t paste into the track for you, you could try pasting it to an empty part of the screen, then Tracks > Align Tracks > Align End to End, possibly followed by Tracks > Mix > Mix and Render.