Yes, Pinholemaster has it right. You match the aperture on your camera to the color on the sensor scale that matches the color on the distance/film speed dial. You will have a choice of several f-stops, depending on the fastest aperture your lens provides.
For outdoor fill flash, check to see what aperture the 283 is calling for, make sure the sensor dial color matches, and then if you want a "-1 stop" fill, set your lens for an aperture that is one stop smaller: example, 283 says to use f/8, and you want a "minus 1-stop flash fill", set your camera lens for f/11.
Also, when I want to use an lens aperture that is 1-stop wider/bigger/faster than the 283 calls for (and that aperture falls in between choices on the 283), I put a white handerchief (only one layer, light cotton) over the flash head. If I have one available, I'll use one of those "wide angle" diffusers they make for flash heads. A piece of frosted plastic like you find in wallets for holding credit cards also works. Test it to be sure.