You usually get introduced to it by your academic supervisor or collaborators as a masters or PhD student. If you're a solo researcher who has made a significant contribution on the frontier of science, I'm sure you'll be able to understand how Arxiv works as well. Because I assume you have had some conversations with other experts in the field. If you're a full on autodidact with no contact to any other researchers in the field, well, maybe it's better if you chat with some other people in that field.

Its reasonable to have a tradeoff here to avoid cranks and now AI psychosis slop. You can still post on research gate and academia.edu or you own github page or webhosting.