Hello treehugger!
You can read about the Acorns here:
http://garden.org/special/acor...
And, you can purchase the cute little "microbadges" for 5 acorns apiece on your profile page under "Your Actions": manage your microbadges; browse and add badges! Please don't hesitate to ask any questions ... I'm not too good at explaining things but we're a very friendly bunch here and someone will always know the answer to questions!
to terrafirma too!