That was very helpful, thanks! Last time, I did something wrong and got a weird result, therefore dismissed this function. But this works perfectly and now I understand what it does.
Though still it’s distorted and wrongly rotated. Ok with [Ctrl+P] it automatically aligns it 90° then I can rotate without issues. But still the faces are distorted in their size. DO I need to manually move each vertex ?
(Forgive if these are beginner questions, but the tutorials I did only covered the basics of unwrapping)