On my 1992 XJ, cruise control does not work. It could be that I am not using it properly, since the text that says the switch position is badly faded and unreadable. So how would I use it?

The first place I would start is the vacuum line that goes to the vacuum res in the bumper.
If you are getting good vacuum, then the next place to look is the combination switch on your steering column. Those wires get old brittle, and often get pinched in the column it's self.
That switch is very easy to replace.

Been a while since I've seen one but the bottom on the end sets the the speed and depressing it should move the on/off switch to the on position if it happened to be off. If setting the speed and it's in the ON position there is likely a vacuum leak as the cruise motor is vac operated. Usually suspect is the vacuum reservoir in the bumper or the lines connecting to it.