Contributed by B@rt.
Empties are 'helper' or dummy objects - they are not rendered but they otherwise have all properties of a normal objects: you can animate them and include them in object hierarchies. Empties are very useful for creating groups of objects; select the objects that you want to group, hold SHIFT, select the empty and parent them. You can now control the whole group by manipulating the empty.
To add an empty, bring up the Toolbox and select Add>>Empty.
Contributed by B@rt.
To convert a surface or curve to polygons select the object and press ALT+C. Please note that this will replace your original object!