im not quite certain as to what the difference between a mixer and say editing software is. im aware the mixer is a piece of external hardware but is it a necessary piece of equipment for a beginner?/ when would it be?
Most editing software allows you to have multiple layers of audio. You can mix & change the levels of each layer separately, to make some louder or softer than others, with the software.
I think the OP was referring to a video mixer rather than an audio mixer.
The main difference is that a video mixer is generally used for cutting and crossfading between multiple live or pre-recorded video sources in real time. Editing software is not a real time thing.
You would use a video mixer (or switcher) if you were doing a live broadcast with multiple cameras or a camera and additional video.
Editing software would be used in basically every other situation. Video mixers don't have a very prominent use in filmmaking