Mack,

can someone tell me how i do this in soundforge

SoundForge has high-pass and low-pass filters built in, so you don't need to
buy anything further.

in instruction number 4, "splice the audio so that you cut out all the
non-vocal parts"

What exactly is the goal of this exercise? Maybe there's an easier way to do
it.

I agree those instructions are less than eloquent. But you seem to not have
quite enough experience either. Splicing is an ancient term, from back when
audio was edited by cutting physical pieces of tape. You can do exactly the
same thing by cutting and pasting in SoundForge. And if you screw up,
instead of losing your only good take as pieces of tape collect on the dusty
floor, you can simply click Undo.

--Ethan