The palette in the function block editor allows you to drag and drop function blocks, graphics, and parameters onto the function block diagram.
From the palette, choose the category you need (Analog control, IO, Math, Special Items, and so forth) and select the icon you want. Drag the icon to where you need it on the diagram.
You can customize your palette by adding new blocks, making a new category of blocks, or making a custom category of the blocks you use most often.