OK, great, Win10, got it 🙂
1) I think you might be talking about the area in the x-sheet that’s called “annotations”. In there you can scribble notes, draw charts or arcs or arrows or whatever. Also plan dialogue by writing out phonemes or letters. Mark key drawings and breakdowns, etc, etc… Just notes, like they did in the old analogue days too.
2) When you import an image or a sequence of images (video or animation), it automatically comes in as a reference layer. You can not draw on it or copy it to a normal layer. The only thing you can is copy/paste reference frames around, drag out clones, etc – everything regarding timing. What you import is bitmap (aka raster) images. You can draw “on top” a reference layer, by just adding a normal layer on top and draw there. When you draw inside AP you are able to rotate and not least scale your drawings or parts of drawings without loosing any information or getting any degradation or blurring.
3) Normally you would be back in draw mode when you get on to a normal layer – you might have been in some mode or had some tool selected since it didn’t happen for you. Or it could be a bug. Please keep and eye on this behaviour if it happens again. Thank you!