Question about a note I'm not familiar with

What am I supposed to do with pair of grey arrows pointing down? I’ve been looking and I can’t seem to find anything about them.

I have no idea how you encountered that at random because no one uses those, but they are lifts. You need to already have your key pressed, and then release your key when they are over the receptor. They are really only seen in certain files (mainly .osu imports with a setting enabled) for release timing. Lifts on their own are really strange and you really shouldn’t be seeing them in files you play.