Every VRML viewer is different in terms of the controls it provides and the methods by which you manipulate the virtual objects or maneuver yourself through them. You will have to play with the controls or click some kind of help button in yours to learn what happens. You may wish to lock the object in place (perhaps with a button labeled examine or flip), and spin it around, perhaps moving it closer or further to adjust its size in the viewer window.
Some viewers nicely allow you to give objects a spin, after which they keep spinning as if they had inertia; in others you must hold down a mouse button (or an arrow key) to keep it spinning. I hope other viewers add this "inertia" feature.
If it is an option, polyhedra look better if you choose flat lighting rather than smooth lighting. Some viewers do not appear to have a flat lighting option, so everything looks rounded like a polyhedral pillow.
You may have a "wireframe" viewing option which eliminates the faces, showing just the edges in space. Extra lines are visible in some viewers because the faces with more than 3 sides are broken up into triangles for rendering.
If you are running on a slow machine and the motion appears jerky, try shrinking the size of the window, so the program has less so draw in each frame. Also, flat lighting is faster to compute.
To make a side-by-side comparison of two solids, open a new window and put one model in each. Some browsers let you click on a link with the right mouse button and select open in new window. In others, look in the web browser's file menu for new to create a new window. It is also handy to open a link to an object in a new window if you will want to keep reading the text while looking at the object.
Going inside the polyhedra is a big part of the fun. If your viewer doesn't let you, look for a menu option which lets you turn off collision detection, so your motion doesn't stop when you hit a surface. If you get inside but see nothing, it could be because your viewer has a backside culling option turned on, which lets it draw only the front of each polygon. Turn the option off.
Currently most (all ?) VRML browsers have a problem with self-intersecting faces. The 3D software does not know how to break them apart properly into triangles. You can read what I have done about pentagrams.
Setting your screen to high resolution and high color depth (more than 256 colors) will make things look better.