Always backup your mod files before using this tool. It's still work in progress. It shouldn't cause any major damage but there's always a chance I made some mistake. Better be safe than sorry.
Instructions:
First you need to load your files. In the first window that appears after running the editor you'll need to enter paths to your game and your mod directory. You don't need to provie a mod directory or game directory if you provide all the files needed below.
The mod directory doesn't need to be in the mods folder in documents. It can be any directory given that right inside it you have all of the needed directories (common/, history/, map/ etc.). If the editior detects that some of the files are missing, it won't work. Here you can also check which files you want to use. You can stick to the game files, trying to edit those in case of province history and country history will result in new files getting created in your mod directory. Editing everything else while it's set to readonly will result in no changes being made to the files. After checking everything, click "Confirm file usage", loading window should close itself and a new one should appear, describing what is currently being loaded. After some time you should see the proper editior.
If you don't see the map in the middle, just click on it, it's a bug with refreshing.
You can use WSAD to move on the map.
You can use LMP to select one province and RMB to select many provinces. Editing province info while having many provinces selected will result in changes being applied to all of them.
Most of the buttons are self explanatory but I will provide a detailed manual in the future.
Saving province history and country history is done through the last two tabs. First you need to keep your changes in "Changes" tab. Then you need to save the files in the next tab.
Trade nodes, areas and everything else has a separate save button for now.