I don’t think one simply understands FLCL. I didn’t like it — I couldn’t find anything I enjoyed about it. I can appreciate what they were going for even if I don’t fully understand it. I would say it’s better for someone who has seen more anime and understands the cultural tropes. Not something to jump into if you’ve seen a ‘starter’ anime (something like My Hero Academia, Sword Art Online, or the like) and are looking to go deeper. But definitely something to check out eventually. Fortunately it’s short.