the raven 1.4 version of Radiant should be installed to it's default location with the JKA specific files in the JKA folder. You may need to reinstall. Also, make sure GtkRadiant is in JKA editing mode.
As to finding the bsp, you have to compile the map, which rich deisel lists in section 102 lesson 2. Don't rename your .map files, this just changes the extension that windows sees and does nothing to make them playable in game. .map files are basically a list of every object (by origin, vertex, name, edge, etc) that you have placed ingame. a bsp contains much more data. consult your manual/help in radiant for info on all kinds of stuff like this (Help -> manual, or hit the F1 key)
A texture is a file that is a picture. These 'pictures' are what cover the polygons in the game. A shader is a text file that modifies a texture in some manner. Shaders can do ton's of things, make the texture move, emit light, or even give the game engine specific hints on how to display the world.