I signed up but have no idea what the job entails and have never attended a homebrew comp. Illumination please.
You will basically be a judge. Comparing entries to the standard for the style. You will be paired with someone with more experience.
That's not quite what it was like when I stewarded. True, I did get to sample a lot of great brews as well as a few not so great brews. I did it because I wanted to see what goes on behind the scenes of a comp before I volunteered to judge. We basically made sure the judges had whatever they needed. That included water, bread, delivering the entries, pulling a second bottle if there was a problem with the first (e.g. cracked bottle), emptying the dump buckets, and so on. Basically you do anything and everything so that the judges can focus on tasting and scoring the entries.