Its dead easy.
He needs to get the console onto the network for internet access. This can be done by connecting the 360 to a router, or using internet connection sharing via a PC. Wireless access will require a wireless adapter.
1. Connect internet cabling
2. Go to your System blade and under network select 'test internet connection' to make sure your on *** network
3. Go to the Xbox Live blade
4. Select create a Live account
5. Follow the on screen walkthrough
6. Connect to live, and your away
When you first create a gamertag, you get a months free gold access, after that its £39.99 for a years access at most retailers, but it can be had cheaper. The gold subscription is what you need to be able to play games online.