First we start the VisualGGPK.exe
You have to select a file , the "Content.ggpk" in the Main directory of PoE.
(C:\Program Files (x86)\Grinding Gear Games\Path of Exile) If you haven't changed that.
After open the file we see this :
With clicks we can open different Points and surf through the File-Structur of PoE in a Tree Style.
There are following sections :
Art - All Images , Texturen, Models etc.
Audio - Everything with sound , Music etc.
Data - Alle information, Questnames , Descriptions, NPC-Texts etc.
Strings, Errors.
Metadata - Interface, Items, Character , Logical Stuff , Alot of Scripts
minimap - Minimap

-Scripts etc.
Scripts - Scripts
Shaders - Shaders
How you can see it's seperated in different sections.
Alot of files you can edit are a kind of database and you can edit them in Visualggpk or export them in the CSV file format. After editing don't forget to save.
It's also possible to export a section like "Data" etc.
Rightclick the Item -> Export
For example you can export the data first edit them with a editor of your choice and replace the original files with the new one's , simply drag n' drop the files/Directorys on the Tree.