Hey - thanks for the response.
So I understand how to highlight the layers, I'm on my laptop right now but underneath the 'body' group in that screenshot there is a layer for the line art and then a layer for the colour (the cream colour on the body at the moment).
When I brush on this layer, I want to ensure that colours don't get painted outside the lineart and onto the background behind it. How can I do this? Do I have to manually trace-select the body colour shape and separate it from the background? Is there a better way of doing this than tracing it with my (shaky!) hand?
Sorry for all the questions, I don't find the tutorials particularly helpful really, i've watched the ones on the affinity site but they talk about editing photos more than illustrating - in hindsight perhaps I should have gotten affinity designer.
Anyway - would really appreciate it you could help me further!