Saving, for now, is done by exporting your map to a folder. Just reopen those files later to make changes. To play your maps, you can either add in a new level to the game or you can replace the files for another level. Look in your LevelsGameLevels folder and find the level you want to replace, then rename your files to overwrite the old level files. Always be sure to back things up first, and also check the level entry in the CFG file to make sure it's loading all of your files (some levels don't load erosion maps, for instance, so if your level has erosion and you put it in a level entry that doesn't look for the erosion map, erosion won't happen).