Here is a brief description. The key switch has a small gear cog on it. When you turn the key this gear rotates. The gear is in mesh with a flat piece of metal with gear teeth cut along its length so that when you turn the key this piece moves up and down parallel to the steering column. In turn this piece is connected by a rod running down the steering to the electrical ignition/start switch on the outside of the steering column under the dash.
By loosening the bolts holding the ign/start switch it can be adjusted slightly further up or down the column. Might be worth trying that as it sounds like the key switch is not pushing the rod far enougt to get the "off" position on the ign/start switch.
If that fails then it would sound like something is broken or damaged inside the steering column which will mean that the steering wheel and the column covers will have to come off.
If you do a search of this forum for "ign switch actuator" you will get some great information on how to get into the column. Good luck.