Kate,
I do agree that we have to agree on terminology. For instance, I didn't realize G-drive was a sort of brand name-- I was confusing things like the C-drive in Windows. So I've been working on it:
"Photos" is an app-- it's relatively small, like 0.01GB in size. It has no pictures (notice how I say pictures or images, not photos-- the app name causes confusion!) The "Photos" app is in the Applications folder, and its icon is also in the Dock.
To "Open Photos" is the same thing as to "Run the Photos application." You can run Photos by clicking on its icon (in the Dock or in the Applications folder), by double clicking on the Photos Library icon, or by double clicking on any file that you've designated to be opened by Photos.
Also, Photos can be told to open when a camera or an SD card is connected. Or it may be that an app called Image Capture (which lets you put pictures places other than Photos Library) opens when an SD card is inserted. Or some other app opens. That's why I'm asking for details. When you say "import on to the external drive" I'm not sure which app is doing the importing.
The "Photos Library," 1 to 100 GB in size (or more), is where "Photos" stores all the pictures and information about them. The "Photos Library" (default name is "Photos Library.photoslibrary," but I have one named Ireland.photoslibrary, for instance) is originally created in the Pictures folder of the user account. But the Photos Library can be anywhere you want on the internal Mac drive, and it can be on an external drive as long as that drive is connected by a cable (not a network) and is "Formatted for Mac" so it can support the features Photos is looking for. And the volume must never have had Time Machine on it since it was formatted.
"iCloud" does lots of stuff. Here in the Mac Photos forum we usually mean "using iCloud.com to synchronize the Photos Library across macs, iPhones, and iPads." But iCloud also has email and other stuff, including a virtual disk drive where you can keep files and folders. So if someone says "I put that picture on iCloud," we may assume they mean iCloud Photos when they meant "iCloud Drive." These things do get so confused in conversation!
So when you say " These images appear also in iCloud," do you mean in the synced Photos section of iCloud.com-- the cloud app that looks pretty much like Mac Photos? or something else?
Sorry about the length and possible silliness of this-- I just thought we might be meaning different things from the same words.