Aside from creating scenes, Behaviour is quite easy to use. To start Behaviour, you must be able to supply a datafile. You probably will not want to create one yourself the first time, so just open the "datafiles" folder, and pick one. If Behaviour was successfully installed, it should start as you double- click the datafile. A window (or several, but probably just one) will open, and that's all there is. Alternatively, you can drop a datafile on the program file, or you can start Behaviour from the shell with datafiles as arguments.
To manipulate Behaviour, you use the mouse (and keyboard sometimes). There are two modes of navigation in Behaviour. Both of these use the left mouse button for orientation, and the keyboard for movement. The easiest way to find out which one is active is to just click and drag with the left mouse button somewhere on the window. If the scene starts rotating, the orbital mode is active, if nothing happens, or the camera switches view, the lookat mode is active.
In the orbital mode, the left mouse button controls rotation. Dragging from left to right orbits left to right, up and down orbits up and down. Holding both mouse buttons or using the third mouse button "rolls". Pressing "1" zooms in and "3" zooms out. If you use the numeric keypad the keys might seem more logical.
If you click and drag on an "object" (the specific definition of object is explained in the documentation, it doesn't really matter what it is though for now) with the right mouse button, the object will be dragged along.
Everything else is performed automatically by specifying instructions in a datafile. I suggest skimming the documentation and then studying the example files in the "datafiles" folder.