Actually, while Strobist is nice, you might have some problems adapting the content to your Yashica. Thing is, the flashes on DSLR's are often used in TTL mode (through the lens). This is an automatic setting where the flash is entirely controlled by the camera. They also use either pocket wizard wireless triggers or the flash's internal infrared sync. These flashes make things very easy as you can simply remotely tell the flash next to aunt Bertha to overexpose by 1 stop and tell the one next to cousin Ernest to underexpose by 2 and let your fill light at -1 so that the daylight will still show through..... and stuff like that.
On the Yashica, you have to make sure the flash sync switch is on X. Connect the flash through the PC cable, select a shutter speed (they all sync since it's not a focal plane shutter). Then you set the computer on the flash to 100 ISO, focus, read the distance on the knob, report this on the computer, read the aperture and set it on the camera. That simple.
Or, if your flash has an automatic mode, you just set it on auto, put the dial in the proper position, check the required aperture and set it on the lens. That's it. The flash takes care of the rest by using its built-in light sensor. That's what I do on most toy cameras and the exposure (almost) always comes out OK. The good thing about this is that you don't have to focus and adjust the aperture by hand. That way you can work a lot faster.