The preview is the theatre where all your masters and instances perform.
Select layout and drawing options from the menu.
In the sequence layout all the selected masters and instances are on a single line. They appear in the order you’ve selected them in. Command 1 to select.
In the stacked layout all the selected masters and instances appear on top of each other. Command 2 to select.
In the lined layout all selected masters and instances appear on separate lines. Command 3 to select.
Command y switches between filled and stroked drawing.
Control clicking on a glyph gives you an option to copy that glyph in GLIF format. This allows you to paste the shape directly into RoboFont (and other apps that support GLIF data on the clipboard)
Selected glyphs also show indicators for contour and point indices.