Map Art is where, in Illustrator CS5 (and above), you use the 3D effects (EFFECT...3D...Extrude & Bevel/Revolve/Rotate). It is where you 'wrap' an image or texture around your 3D shapes.
To achieve this, you need to save your image or texture as a Symbol. (How? See this).
If you are drawing the object to be 'mapped' using the standard tools - Pen Tool, Shape Tools etc., Illustrator uses corner anchor points to define a new surface. Smooth anchor points will not define a new surface. When drawing your art, carefully specifying where corner or smooth anchor points appear on your path gives you greater control over how many surfaces are created and where they appear.
You should seelect all the components of the object you wish to apply a 3D effect to by dragging the Select Tool across it and then Group the objects (Ctrl. + G)
In order to map artwork onto the surface of a 3D object, you must first apply a 3D effect to an object. Then, from either the 3D Extrude & Bevel Options dialog or the 3D Revolve Options dialog, click the Map Art button to bring up the Map Art dialog. If the Preview option in the resulting Map Art dialog isn’t checked, go ahead and turn it on so that you can see what your mapped artwork will look like as you make adjustments to it.