Merit is something given to members of bitcointalk for being helpful. Trust points? Pretty much like feedback points like you see on sites like eBay. It has nothing to do with bitcoin itself whatsoever. So yes, you can freely buy bitcoin and freely use the forum and converse with people without merit.
More information on merits: https://bitcointalk.org/index.php?topic=2818350.0

I always suggest reading this compilation of guides to total beginners. It should keep you busy for a while: https://coindesk.com/information