Thanks Leonie and Yer-man I appreciate you taking the time to respond.
I took my ipad to my Art class today and was able to find my photos (the subjects of my painting today) fairly quickly using my structure of folders and albums - excellent.
I apologise for the term "sub albums", perhaps should have used the term "level" that may have been more descriptive. I used to create and manage databases in a previous life and operate Project Management Software (level driven) , and write code too (also level driven before OOP code) - sadly missed! so I do understand hierarchy, I just have to understand the "apple way". No sweat.
To follow Leonie's analogy, levels would be the branches of an upside down tree, as each branch splits into other branches then sub levels are produced. Level 1 album, level 2 album, and the albums at each level would sit in container folders (as Yer-man stated). You can also have Level 1.1, 1.2, 1.3 2, 2.1 etc but that another methodology (work breakdown structures or document breakdown structures).
The issue I had: Adding photos to an album(target) from another album(source) in perhaps a different folder.
The reason I wanted to do that, was because the lower level albums have fewer photos in them and therefore easier to search through and find what I want.
Silly Solution: When I opened the target album and clicked create, all I saw on my screen was the list on the left "Photos", days, people and pets, memories.... etc etc etc. Ah... but I'm forgetting the modern way. i.e. scroll down endlessly in the hope you'll find something to improve your day, so I found I could scroll down the list and there way way down was "Albums" (oh joy!) and of course I was able to navigate within that very quickly and find the photo from the source album.
Great and problem solved.
My next job will be to get all the clutter off the screens, things like "wallpaper suggestion, featured photos" belong somewhere else, I'm sure some of its useful (really..), but I like to decide what's useful to me, ergo "albums, favourites" right at the top of the screen.
..... and after that tame the beast, to start with, teach it to stop from starting random slide shows and playing random music, it disturbs my fellow members of my Art class!
Many thanks again both for the help. No need of further discussion.