So yeah, could anyone explain how to use goodbox's torso template and also the panorama torso template, both of which are provided in nblx's tutorial.

Help is really appreciated. TY

In about 50 steps with a lot cut out.

open goodbox's template
draw on goodbox's template, front and back, on new layers.
merge new layers
quick select the active pixels that are for the torso to get the selection (or however you get the selection of the L_pecs or whatever)
copy both the front and back from goodbox's to nblx's template in the right spots and resize (self explanatory? back-side-front-side-back, this doesn't really take into consideration stretching and different size parts so be careful about that)
fill in the smaller squares in nblx's (sides)
-optional- edit nblx's template a lot to make it full seamless for the top and bottom.
once its drawn on nblx's template then move it all over to the main toribash template resizing and rotating sides to the right spots.
repeat 6 more times for the other parts of the torso.
kill yourself because mapping torsos suck.

I probably left out a lot of steps but that's the main idea.

wouldn't resizing so many times literally kill the quality?

kinda. but goodbox's template is 2x bigger so its always downsizing, and when it squishes it onto the pecs the pixels get squished back down ingame so you dont notice it that much. just dont do really fine detailing (1-2px) till the very end.