How do I insert a flag onto a nation using the Country Creator Tool?
You can use the flag tool to convert from PNG to the correct file format and sizes, if you haven't already saved as a .tga
Once you have done that, name your flag files TAG_IDEOLOGY (or just TAG) where TAG is the tag of your nation, and IDEOLOGY is the ideology that flag design is for.
Then move those files into your mod's gfx/flags folder.
If you used the flag tool to to generate the flags, the files with "small" and "medium" in their name will need to be moved into folders gfx/flag/small and gfx/flag/medium, respectively, and have the word small/medium taken out of their filename.
At some point, I will make the flag tool a little more easy to use/export files in the correct structure, but that will come as part of a bigger overhaul to how it works, to make it a little easier to use, and look nicer.
Then upload your flag using the flag tool, and download the files it returns, and put them in the correct flag folders.
More can be found on flags here: https://www.youtube.com/watch?v=OjrD3u-OTgI