Hi - firstly, my apologies for asking what I'm sure is such a basic question.

I'm completely new to Krita and I'm trying to understand if I've chosen the wrong tool to use with my graphics tablet (I'm only doing diagrams in meetings).

I really like Krita, the layout of the menu's and the options. I just can't erase, without having to revert to Undo! That's all I really want to do. The issue is the fact that the eraser erases the background and not just what's drawn on the background. In short:

1. I create a new file with a White background at 100% opacity (layer 1)
2. I lock that layer and duplicate it (to make layer 2)
3. I draw on layer 2
4. Decide that I want to erase something so I choose the eraser tool
5. The eraser then removes what I've drawn but also removes the background
6. I obviously cannot (and don't want to) draw on layer 1 so now I'm left with a transparent area on layer 2 that I can't re-draw on

Perhaps this is just how paint tools work and perhaps I need to look elsewhere for what I need but I really like Krita. What am I missing?

I just want to be able to draw something, erase it and then re-draw over that same area. That's literally all I want to do. Can anyone help?

First of all, I'm puzzled about what you actually see because repeating the steps you describe, I can't notice that the white 'background' of layer 2 is being erased, because all I see is the white colour of layer 1.
(If you locked the first background layer and Duplicate it, to make layer 2, you'd need to unlock layer 2 to paint on it but you don't mention that in your numbered stages.)

Secondly, this is not how things are usually done. If you've created a new image, and haven't changed the options on the Content tab of the New Decument window, then you'll have Background as a raster layer (painting layer) and it will be coloured solid white.
That is intended to be 'the background' of your image .

Then, the usual thing to do is create a new paint layer by clicking the large '+' icon at the bottom of the layers docker.
That will create a new transparent paint layer that you are intended to paint on.
If you paint on the 'Background' layer (the first, original one) then erase, you will erase paint and then it will be transparent in that area and you'll see the checkerboard pattern, that indicates transparency.

Also, the 'background' layer is special in that its white colour extends to 'infinity' so that if you resize the canvas to make it bigger then it will still be white at the newly enlarged border. This is why it's not a good idea to Duplicate the 'background' layer and use it for painting on.

This situation really needs full screen screenshots which are inconvenient to post on this forum.
It would be better if you go to https://krita-artists.org/ then sign up and log in and start a new topic that describes your problem. You can easily upload screenshots there.