When you export an image of a graph, or comma-separated-value data file, the file is saved by default as a download. Where that download is saved is up to you.
When using a Chromebook, to easily work with the image or csv file, we recommend saving it directly to your Google Drive.
1) Choose Export from the File menu (the page icon), and choose a .csv data file or image as needed.
2) In the resulting screen, choose your Google Drive, navigate to your desired location, and give the file a recognizable name.
3) Click Save.
Now you have a file, of recognizable name, stored on your Google Drive, which can be inserted into documents or spreadsheets.
If you did not explicitly choose a storage location during download, the file is probably stored locally on the Chromebook. Here are the steps to make it accessible, so that you can, for example, insert it into a report:
1) Sign in to your Chromebook (you probably are already signed in)
2) Click the app Launcher (looks like a white circle in lower left corner)
3) Select Files (its icon is a blue circle with a white file folder)
4) Select the Downloads folder
5) Select your file, then drag it into your Google Drive folder. The creation time of the file may help identify it.
Now your file is accessible on your Google Drive like any other file.