Okay, seems the trigger requires variables that doesn't exist before you import, even after you import, so first, go tick the "Create Unknown Variables when Pasting Triggers Data" [Screenshot later]
Second, you need to make sure every custom resources that used in the trigger has already been available to your map
About JASS and MUI
JASS as Hell_Master stated, JASS is the true language of WE, which is actually a big script that is replaced by Triggers that is we usually newbies use at WE, called GUI [Explanation Below about GUI] JASS is hard coded and takes time to master [only good script coder can master it in matter of weeks, it usually takes months to master it] JASS is also allowing you to use full extent of WE itself, because some JASS trigger aren't accessible via GUI
GUI this is a short term of Graphical User Interface, it has nice look and easy to understand than JASS, but it has many limits and can easily leaks unless removed via some leak removal script.
MUI MUI is a short term of Multi Instance Castable, means no matter how many unit is casting the same spell that uses the Same trigger, it won't bug and play correctly, in addition, wait command aren't allowed for spells that is going to be used by multiple units, also, there's another term related to this, called MPI, which explained below, one more word, for some reason, wait is still possible to make trigger MUI, but in a small case, read it
here
MPI MPI is a short term of Multi Player Instance Castable (AFAIK), means that even 10 players cast the SAME ability with the SAME trigger and at the almost SAME time the ability won't bugged, from my knowledge, MPI also restrict Wait command, but both MUI and MPI can use artificial waits, which can be read
here