To create basic geometry you can be in either the Scene or Developer tab. Right click on either the Scene root or an assembly that you have created.
From there you can go to Create > Geometric Shapes and then click on the shape you want. From here if you right click on the shape you can then click on Show Properties, from this window you can use the PRS properties to adjust the position, rotation or scale of these objects.
Whilst in the scene you can also click on an object to display the PRS Manipulator, if you click on an object and the manipulator doesn't appear, press the F9 key and this will enable it for you.
There are several methods of controlling the 3D scene, the best way to learn about these is by going to the Visionary Render Manual or the Visionary Render Help (F1) and going to chapter 8.3.1.
Another way to navigate the scene, or focus on one specific object you can right click on it in the scene or in the tree view and select the option called Fly To, by using Fly To this will fly the camera to a position where the full assembly is visible (unless obscured).
Finally, you can create several preset camera positions and use these in conjunction with the Fly To option to quickly navigate to ideal views. In order to create one of these Viewpoints move the camera into the position that you want it, following that go Scene Tree > Right Click (on scene root or assembly) > Create > Viewpoint. Once you create this viewpoint it will automatically take on the position of the camera. You can also adjust the properties for a Viewpoint the same way that you can with geometry.