Without going into lenghty explanations, suffice to say that on a typical ILS approach, you adjust the speed with the throttles, and stay on the glide path with pitch inputs. According speed, you will then have a certain ROD as you are on a constant angle (or should be...) during the approach. As for the autothrottle, it all depends on the aircraft flown, the company's SOPs and personal preference. If weather permits, I like to switch all off, the goal being not to use the airbrake until on short final, and using as little as possible throttle movement until retarding them in the flare.
Don't know if that sounded like an explanation, but at least I tried
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... cut my wings and I'll die ...