How do I give a user permission to access external drives?

The account I primarily use is not in the sudo group, and this is intentional. An issue I ran into is that I don't have permission to access my external hard drive. Here's the message I get.

This location could not be displayed.

You do not have the permissions necessary to view the contents of "1TB Storage"

I'm not at all familiar with BASH or Linux, I've only ever really used the GUI. But I assume that I have to log into my admin account which is part of the sudo group and give my primary user access to external drives, but I'm not sure how I would do that. What commands would I use? And would I be able to give my primary user access to external drives in general, or would I have to whitelist specific devices?

(In case it matters, I believe the HDD is using the Ext4 file system)

If you are plugging in an external hard drive or USB stick and do not see it on your desktop, this documentation might help; specifically the bit on user privileges:

If your usb device doesn't appear on your desktop, you should check that your user has the correct privileges. Go to System->Administration->User and Groups, choose the user, click on "Properties", then go to the "User Privileges" tab. You should have the "Access external storage devices automatically" option checked.