I have got many files locally (which are in my downloads folder) on my Chromebook. But, how do I sync those files to a google drive account other than the currently logged in account?
EDIT: this did not exactly answer the OP's question so please ignore.
1) Using the Files app, copy the files and folders to be moved to a temporary folder in your Google Drive.
2) Right click on that folder and click Share. In the pop up window enter the account to share with and click Done.
3) Login to the account you want to share with either by adding the account to your chromebook or opening an Incognito window and logging in there. Go to the Shared with Me part of the Google Drive site
4) Copy the shared folder into your Google Drive.
It's not the most stylish/ideal option, but you can download the Google Drive app from the Google Play Store, open it up and log in.
Then navigate to the Files app and right cick (two finger tap) on a file and select more options and then you'll see a save to drive option, where you can save to as many different google accounts as you like.
As for opening from Google Drive, just navigate to the google drive app you just installed from Google Play, and use that to navigate/save files to your Chromebook.
It's not the most stylish, I'll admit, but it does the job if you don't want to keep switching between user accounts!