Rainbow Painter basically consists of a picture editor/viewer in the center, with a number of panels (see below) around it.
The static windows scattered around the large picture editor/viewer window are called panels.
There are three groups of panels and they can all be switched on/off by (un)checking the check box with the name of the group.
At the top you have the Menu Bar Panel, where most of Rainbow Painter's functionality can be found in familiar menus like File, View etc.
On the left side you have the Main Panels, consisting of the Layer Controls panel and the Tool Settings panel.
At the bottom of the screen you have the Extra Panels with mostly palettes and some things also found in the Menus.
The Extra Panels turn into a Zoomer when the mouse pointer is over the image.
As you may have noticed, this manual doesn't cover every last nook and cranny of Rainbow Painter.
That's where the popup-help comes in.
Whenever you're wondering what a button does, just hover the mouse pointer above it for a couple of seconds and a short explanation will (in most cases) appear.