Boy, the Surrender-crats sure are having a topsy-turvy week. I bet this strategic blow by Iraqi "freedom fighters" almost makes up for that "lousy" news about the economic rebound. More opportunity to convince the public that the only alternative is to run and hide behind in-effective UN appeasement-mongers. Funny how their goals seem to mesh with Saddam's.
Mortars are high tajectory artillery. Though they can be very large (and were historically), most in use now are quite small. In WWII the Japanes had avery light one that was fired while being held on a soldiers knee.
They typically throw a bomb ranging from the size of a hand grenade to 5 or so hand grenades.
They are extremely simple consisting of a piece of pipe that is stood near upright, often with two legs. The bottom of the pipe has a pin in its centre. The mortar round looks like a very small bomb, and has the propellant in its base (in light mortars the propellant is like a shotgun shell). The bomb is dropped into the tube, the pin strikes a percussion cap on the bomb that ignites the propellant and the bomb is propelled up and out of the tube.
http://www.fas.org/man/dod-101/sys/land/m224.htm Has some pictures