Creating a new file involves:
The first two should be fairly self-explanatory; the type of file you are creating will dictate which application you use, and creating the content is up to you! However, when you save a file for the first time, following these steps should ensure that you can find your file again:
Once you have created the file, simply pressing Ctrl-S (or going the File menu and choosing Save) will update the saved file on disk.