I would say the easyest way to find out what to do would be to find someone with Heli experiance to help you (a local club maybe), go over the Trex , and explain the 1,000,000 things that you are going to have to know.
If you cant find anyone then read read read.... first go to HeliFreak and watch the Trexx build video's and go over evrything on your bird. Then start googling questions you have about the3 radio to find as much info as possible and post questions you have here. There are a lot of very helpful, knowlageable and freindly people here( its funny the 1st 2 to resond to your post are the 1st 2 that came to mind) and get yourself a computer flight sim that has Heli's , flying the Trexx will be a lot different than flying the lama.