How can I draw shapes other than cubes with x3dom? For instance, one shape I want to draw is a semi circle/cylinder. I can only find documentation to draw a cube which I already do. I have not found good documentation yet for x3dom.
X3DOM actually just wraps X3D. So you may better start with the X3D documentation. A quite good overview can be found here: X3D Slides.
There are some other primitives provided like:
<Shape>
<Sphere radius='1'/>
<Appearance>
<Material/>
</Appearance>
</Shape>
Also the examples provide a good starting point.