You really need to have a pattern or someone show you. S&W is not a fussy cut pattern.. actually pretty precise to get it to match up right.
It's a matter of how you cut and stack the repeats. Then you cut with a ruler the size you are using.. this is determined by the pattern.
My first one I did take a class on and that helped alot to understand what they are doing. After the first class I have done several with the pattern books... I use Bethany Reynold's but I think there are others out there..