You'll notice in your post that, underneath your Username and User Title (in your case, Junior Member), your Join Date, number of posts, Bells, and 3DS Friend Code are listed. The relevant thing here are the Bells. The forum currency here are those Bells, and users commonly refer to them as TBT. Technically BTB would be a more sensible name for the currency (Bell Tree Bells), but TBT is the phrase that took off and became popularly accepted.
You can earn more bells by posting. The longer and higher quality your posts, the more bells you can earn per post. The highest amount of bells you can earn per post is 10. Just be sure not to copy and paste things just to earn more bells quickly, as it's frowned upon and could land you in trouble. You can also earn bells by participating in forum events (presumably, there will be an Bunny Day/Easter one soon as there has been one in previous years) and completing challenges, earning collectibles and selling collectibles you don't want. Additionally, you can operate your own shop, whether it be for art, Pokemon, or Animal Crossing items or villagers where you can sell whatever it is that people might want.
Best wishes and enjoy your stay on the forums.
