I am a total Newb: The manual says: "You can start making vector graphics by first making a vector layer (press the arrow button next to the + in the layer docker to get extra layer types). Then, all the usual drawing tools outside the Freehand, Dynamic and the Multibrush tool can be used to draw shapes."
There is no "+" sign on my Layer Docker and I find no way to add a vector layer.

The 'Layers' docker has a '+' symbol at its lower left corner.
If you don't have an image open then the entire docker is greyed out and that is the only situation I can think of where it wouldn't be there.