If you are familiar with YAFL you will have no trouble navigating, it works almost exactly the same way as on your GP32.
Move the directional pad up or down to move through different screens if available (indicated by an arrow in the upper right corner of the screen).
Pressing B opens a category menu, use the directional pad to scroll through categories, press A to select or press Select to cancel. Pressing Start will download the icons in the category you are viewing.