No worries :) It's roughly that agender people don't identify as either man or woman, but as neither. They might not even feel like they have "neutral" gender. It's more "404: gender not found", which doesn't fit neatly into a binary gender system.

Sex and gender are different. Sex is biology, gender is cultural/social. My doctor might need to know my plumbing, hormones, and chromosomes, but my coworkers don't. Someone's perceived sex at birth gives them their 'default' gender, but they might end up not being that gender when they're able to voice their own feelings on the subject.

(caveat: I do not speak for all agender people, non-binary gender language evolves, it can be wibbly-wobbly fuzzy at times. Also, I do see myself under the Trans umbrella because 'the more the merrier' and there's no need to fragment the non-cis community. Alternative definitions of "trans" can be broader, and include "anyone who doesn't identify with the gender assigned to them at birth")

Edit: this instagram post sums it up nicely https://www.instagram.com/the_crafty_queer/p/CzqzG4oOf-8/?img_index=1