they are called G points where u earn from XBL games achievements.There iss nothing u can do with em,they just appear in your Gamertag so u can brag how good gamer you are!
They have no real value, the only purpose they serve for me is a permament, one-stop record of what I managed to do in games on my phone and my 360. For me it's less about bragging but more of a permanent "medal" for myself.