There are a number of thoughts on how to best “grip” or “hold” the rod. This is the one I suggest that you initially learn. I know many instructors who begin by teaching the finger pointing grip. They do this principally because this method of holding the rod minimises the use of the wrist – which when starting fly casting is a generally a good thing.
Ultimately through this course you will learn many different grips, consequently I don’t think it matters too much which grip you initially learn but this one has served me well. In the USA and UK most instructors start out by teaching this thumb-on-top grip. In Continental Europe it is more common to begin with a finger pointing grip.
You can read more about grips in the Manual: http://www.sexyloops.com/flycasting/tgrip.shtml
[The Fly Casting Manual was written back in early 1999 and I do not agree with everything I wrote back then!]
Got a question on Grips? Try asking here: http://www.sexyloops.co.uk/theboard/viewforum.php?f=36
Alternatively please send me an email paul@sexyloops.com