I few folks gave me an acorn when I joined and or when they connected with something I posted. It said Welcome in a concrete way. 5 acorns are given when you join. Read the info to learn how to get more if interested.
Older members understand new folks don't have many and may not be able to reciprocate initially or join a raffle, etc.
Acorns can be used to purchase badges --which sort of describe you ..your interests at a glance.
It is sort of a tiny bouquet -- that says thanks...or I appreciate...or welcome...or a way to connect or show that a post reached you in a special way.
The thumbs up is a way to say I get it or I agree or good job if you don't feel like typing..I think it is a way to avoid generating pages of "I agree" on a thread. Just the person who receives the thums up actually "sees" the person that gave it, and so a member can say " thumbs up " showing a sentiment without the collective public eye on them. Perhaps they don't want others to know they agree. I forget to use it and I worry later if the person who just posted before me thinks I ignored them and that I went on to blather about something else-- or that maybe I disagreewith them -- But, can't just keep hitting thumbs up to every little thing. I need to get over that worry. ATP is a very forgiving site ( first and second impression as I am new too) and feelings don't seem to be as touchy..ready to pounce...as other sites seem. No closed off groups --that I have encountered. I think as one new person to another (both being seasoned transplants from other sites) ...go with the flow, and you will quickly learn when to "thumbs up" ..when to part with an acorn ( it will be a while before you have accrue many ) and when to worry -or not - about appreciating the social nuances of the site. I hope this helps!