Hi
Creating materials from textures in ArchiCAD is relatively simple - open the material palette from Options>Element Attributes>Materials. This dialogue is used to create new materials or change existing ones.
Textures are available all over the internet, I found
www.cgtextures.com to be quite useful.
The image you posted probaly isn't rendered in ArchiCAD though - Archicads rendering engine (lightworks) is a dinosaur now and should only be used to create dark and moody goth imagery
you may want to try Artlantis - it's available as a free download which gives you a 30-day trial. After that you have to purchase it, but you can download versions 2, 3 and 4 and still get a 30 day trial on each version.
Plants and trees can be tricky in archicad 0- realistic objects tend to be very high in polygons, so they slow down your model a lot. I always place trees, plans, people and cars in Artlantis.
but if you're wanting to stick to archicad, try these sites for a range of downloadable objects -
http://archicad-talk.graphisoft.com/object_depository.php?
http://bimobject.com/Product
http://archicadwiki.com/LinkCollection/GDLObjectDownloads
a lot of objects are available for free, so browse extensively before buying anything.
hope that gives you a starting point from which to work...
cheers