Very limited set of tools, a pen with a number of fixed width nibs, a highlighter that works in the same colour multiplying way with successive layers as many of the brush tools elsewhere.
The eraser is a bit of a beast in that it deletes the whole "thing" that you tap... I'm guessing each thing is a vector object, and instead of altering it just removes it. There is a clipboard tool which allows an arae to be selected using a lasso tool.
You can zoom in to add some detail, but there are no layers.
Export is not in image format rather as pdf, although you can send a sort of screen shot to twitter.
On the plus side it is super intuitive and you get to grips with it in about 2 minutes, I've used it to capture notes on my course, when we were doing concept diagrams.