On a Chromebook, the location for saving files is up to the user. In the same dialog where a file name is assigned, you can choose the location were the file will be stored. If you choose to save the file to your device, the file will be in the Downloads folder.
Since many school Chromebooks are shared, most often you will want to save the file to your Google Drive and not to the local Downloads folder. To do this, select a folder on your Drive before saving.
To change the default file saving location:
1) Open the Chromebook settings.
2) Search settings for “downloads”.
3) Scroll down to the section with the Downloads header.
4) Choose “CHANGE”.
5) You will see the standard file-selection dialog; choose My Drive, or a folder therein, to default to this location.
It might be convenient to have a folder dedicated to Graphical Analysis files in your Google Drive.