I'm somewhat new to this site and I was wondering how I link my steam account to my profile. It says "STEAM ID" but what is a Steam ID. Is it what you login in as?
It's the number in your community page url, or the custom url if you specified one. Pretty sure both of those work, and probably other forms of the ID but those are the easiest.
If this is your first time logging in after the migration (Feb 8, 2022), you must reset your password to log in. Follow this guide if you're having trouble