screensaver in assembly

HI
I am trying to make simple screensaver because I'm a beginner.
I have thought that it will contain just a letter that will move on the screen. The problem is how do I write so the letter J will move on a screen until I press the Key "A" on my keyboard and the letters stops moving. If I press again the letter J will continue moving on the screen.
The main problem is how do I get the letter J on the screen and how will it move, it doesn't matter how it moves.
Does anyone know? add move outstr????
This code is written in EMacs