Hmmmmmm, Am I missing something? If you have power locks, press the lock button. If not, put the key in the hole and turn counter clockwise. ???? It's the same as every other vehicle I've owned.
If you have had it for a long time and never locked it, the lock may be corroded inside and unwilling to turn. You may have to get some lube inside, and wiggle the key around a good deal before it starts to work. If the key is worn, that will also contribute.