You can find your save files in the following directory;
Each folder is the equivalent of the save file with the same name. If you'd like to share your save file, you'll need to send the entire folder including the files inside of it, such as "Factions.json", "gameobjects.json", "Heightmap.png", "meta.json", etc.
It might be a good idea to zip the folder up first!
For more info on how to find your Castle Story folder, click here for a helpful article.