Just so people are aware --- if you are using the n@owh ui for the fresh classic realms then you should not use the installer. You should instead just copy all of the profiles/weakauras from the text document named "List.txt".
The chat bubbles folder is just a very light cosmetic to chat bubbles to make them more in line with the UI. These aren't needed but if you want them then you drag them to the interface folder.
Whenever you click on the classic zipped file it will have an "Addons" folder. Drag EVERYTHING EXCEPT THE ADDONS folder to the interface folder.
The interface folder is completely worthless and only contains WOTLK addons do not use this folder at all other than to see which addons you should manually download from curse/whereever.
The shared media zip file will go into your interface-> addons folder.
From there you want to go through the list of the addons in the interface rar file and manually download all the ones needed. The only ones that are what I would call "mandatory" for the ui to work are ElvUI, Plater, Weakauras, Details, BigWigs. The rest are just fluff that aren't important but can be installed if you want them.
After that you need to log into the game, open the List.txt file and import all of the weakauras you want. You can find these quickly by pressing ctrl+f and searching for whatever it is that you need. All of the class weakauras are there as well as another super important weakaura called UI Elements. Make sure you get that one from the list. Profiles for the other addons are there as well towards the bottom. I would start with UI Elements and work my way down to the end of the text file.