The icons on the top of the GeoGebra screen are actually menus.  Clicking on the little triangles reveals the menus.The set of menus available depends on which view is active.  It is useful to be able to see the list of icons and what they do.

The full list of tool icons in the graphics view, release 5.0

The Icon menus with labels.

The full list of tool icons in the Spreadsheet view, release 5.0

The full list of tool icons in the CAS view, release 5.0

A full list of tools in the 3D graphics view

PDF version ToolMenu50.pdf