Hi,
There isn't really any way of studying it as such. You can practice it using vehicles, but thats about it.
I did a 4 day course myself in Aircraft and Helicopter Marshalling, from Aviation Resources Training in Stansted.
You can look up the CAA website for CAP637, which is the Visual Aids Handbook, this will give you all the current signals and movements for the UK.
You'll find that Marshalling instructions are different outside the U.K..
Hope that helps,
MRA.