What You NEED To Know
Please read the entire manual/help!
There, we said it.
OK, so we know you'll ignore that, but please consider the following advice:
If you're a beginner, you'll definitely need to learn what 'Layers' (see below) are and how they work.
Even if you're not a novice, you will still need to read about 'Import/Export' (see below), since that's done in a different way in Rainbow Painter.
Imagine having a couple of transparencies (i.e. transparent 'papers' made of plastic), drawing something on them with a marker and finally placing them on top of each other.
That's exactly how layers work, where each sheet represents one layer.
In the Layer Controls panel, the layers are stacked as you'd expect them to be.
Only one layer can be selected at a time and the box situated to the left of each layer toggles whether the layer is active (visible) or not.
At the bottom of the layer stack, even if the picture only has one layer, there's always going to be a 'Paper Color'.
You can change it to the current paint color by left- or right-clicking on it.
If you make a hole in the layer(s) above (e.g. by erasing), the paper color is what will shine through.
Deactivate the paper color by unchecking the box to its left, if you want the picture to be transparent.
You will also find buttons and sliders to change the layer's blend mode and adjust things like opacity.
At the top of the panel there's a checkbox called 'Protect Transparency'. If you don't know what you're doing, then keep this box unchecked to avoid confusion.
If you check the box, any tools and effects you apply will not affect the transparent parts of the layer.
In the Layer menu in the Menu Bar Panel, you can find all layer operations (such as New, Rename, Destroy).
Read more about importing and exporting here.