here, I have 3 vids on session drummer.
it might be worth checking them out.
sonars cake tv also has a few videos as well.
first watch this one, its called basic midi.
http://www.youtube.com/watch?v=k83UVo1OiKA this will show you how to record using something like a keyboard to play the drums.
it uses studio drums but its the same theory.
this is called drum editing in the piano roll.
http://www.youtube.com/watch?v=ruAnAPR6-hQ there is one more as well about setting up session drummer as a trigger device but this actually shows how to set up session drummer properly.
http://www.youtube.com/watch?v=TjZS61Wg-XY these vids were made in sonar x2 but its basically all the same.
the above comments are both spot on, these guys are correct.
the videos will just help with the visual aspect.