1 tbt converts to 200K in game bells technically but you can get by with doing like 12 or so for 2.5-3mil. you can bend it a little but not much. you just post a thread like "selling 10 tbt for 2 mil" or whatever, then put whatever you want in the thread body and then post it. if someone agrees to it, you add them, send the tbt, and they'll come to you (or vice versa) and they'll drop the bells or you can go pick them up.
the "tbt" are this forums currency. kinda like bells in the game but the forums have their own and it's a bit more valuable. they're in the sidebar below your avatar (below the amount of posts you have). you can transfer the money by clicking (say you were giving me some) below my avatar where it says "bells" you click that number right there and put in how many you wanna send and you can send a message too like "for your 3 mil bells" or whatever.