SetActiveTile - active tiles and co-ords in TGB some Q's

Hi all,
have worked through many tutorials and seen some posts, but I need more help ...
regarding parameters...
//%tileObj = %obj.setActiveTile( 0 0, myActiveTileClass, myActiveTileDatablock )

1) how do I determine the location of a tile do I use pickTile(xy) ? what is the xy .. tiles can cover more than one co-ordinate? or some type of %worldPos call.
2) Same xy Q regarding setActive tile ...
3) How do I create a tile class ?

I guess what I really want is a mouseover event and or click ... a strategic map ... mouse over or click city or unit to do something (show info etc) ... so want to test with active tiles ...

Sorry might seem easy to some, but am learning fast and have a prototype game working after buying 2 weeks ago ... just want to improve...
Making a turn based / real time game (make decisions and then it runs until time / action break --> eventually port to 3D engine) and will eventually hope to post some tutorials of my own for newbies...

Thanks Damian