While working in complex artwork you'll often find the need to group the layers or some portions and elements of the artwork in one unit. Group layers come in handy for this, they allow you to make a segregate the layers, so you can hide these quickly, or so you can apply a mask to all the layers inside this group as if they are one, you can also recursively transform the content of the group... Just drag the mask so it moves to the layer. They are quickly made with the Ctrl + G shortcut.
A thing to note is that the layers inside a group layer are considered separately when the layer gets composited, the layers inside a group are separately composited and then this image is taken in to account when compositing the whole image, while on the contrary, the groups in Photoshop have something called pass-through mode which makes the layer behave as if they are not in a group and get composited along with other layers of the stack. The recent versions of Krita have pass-through mode you can enable it to get similar behavior.