I looked into that not too long ago because I had the same question. Some players just rely on normal gameplay drops, while others follow events or community giveaways. When I was trying to understand all the options, I ended up reading this guide:
https://cs2lore.com/free-cs2-skins-2026-guide. It explains several ways people attempt to get free skins and what those methods usually involve. I mainly use it as a reference to see what possibilities exist before trying anything.