Using BB is about as simple as it gets. Look in preferences to set the URL of the image you want to watch and to choose how often to refresh the picture. If the pic you're watching isn't on your LAN, you should be careful how often you reload the image lest your computer and/or Internet connection Get overloaded.
Once running, you can choose whether you want BB to stick on your desktop, act as a normal window, or be always on top. Look in the Window menu for those settings. You won't be able to move or resize the camera window when it's on the desktop. Choose BB's icon from your dock, then choose the option from the Window menu to make it a normal window. Then you can move and resize BB as you like it and stick it back on the desktop to Stay. Of course the URL, refresh speed, and window placement are saved when you close BB and will be restored next time you run it.