Are you interested in how Mosfets work and how to control them take a
look at this short video tutorial:
http://www.youtube.com/watch?v=Te5YYVZiOKs
If you would like a deeper tutorial on the way Mosfets work watch
this:
http://www.youtube.com/watch?v=NSD7n7CR5cM
As a side note: V(gs) is the voltage you need to apply to the mosfet
to the gate with respect to Source in order to turn the mosfet on
which closes the circuit.
I(d) is the current that can flow across the Mosfet from the drain to
source without burning/bubbling it.
V(ds) is the max voltage that you can have across a Mosfet. Meaning
that if you have a 50 V motor connected to the mosfet and the mosfet
is rated with V(ds) of 40V the mosfet will fry causing an open
circuit.
mike