Hi Andrew262. If you prefer to get instructions on the GUI, you have to tell us which GUI you want to use

That's the nice thing about a Posix shell; easy to provide instructions for in plain text, and for most common system tasks, it's pretty much the same no matter what.
I'll take a stab at it, but if you let us know what desktop GUI you're running, that will probably help. You can mount an external drive in almost any graphical file manager, such as Nautilus, Caja, Thunar, Dolphin, and so on. As long as you have one of those loaded, open a window, plug your hard drive in, and then click on it in the side pane of the file manager to mount it. That ought to work.
Here's a screenshot. Notice the little drive icon in the lower left of the dolphin window. I clicked that, and the drive mounted.
https://www.unixporn.pro/i/bM7uLVC.jpg
Try that. If it doesn't work, report back.
If it does work, kindly report back.
Edit: in spite of you preferring the GUI, here's how to do it in a shell:
1. Look at the drives currently attached to your computer:
2. Plug in your external hard drive.
3. Look at the drives again:
The new entry there is the drive you just pligged in. Let's call it sdx (it will probably be sdb or sdc, but I don't know your setup).
4. Mount your drive:
Code:
$ sudo mkdir /storage
$ sudo mount /dev/sdx /storage
5. That's all. Your drive is now located at /storage
You can open a file manager to that location in your GUI by typing in the name of the file manager you use, plus the path. For example:
Code:
$ thunar /storage &