heya, welcome aboard btw,
in order to trade, you exchange 3DS friend codes, (each 3ds has a friend code set up under your friend tab in your DS) and that allows you to play over wifi and interact with other people. in order to trade in acnl, you have to visit a town who's gate is opened! you can open your gate at the train station located at the front of your town. :') either you or your friend will have an open gate and you'll go visit, or they'll visit. this brings your items in your pockets and you're able to access anything in your storage compartments as well! leaving you able to "drop" them onto the ground for your friend to pick up!
tbt or btb is bell tree bell's also known as the forum currency. you currently have 7 btb!
igb refers to bells in the animal crossing games. (in-game bells)