This is explained on the Box.com blog.
The video (below) provides a step-by-stop guide for how to do this.
If you’re technically savvy, you can skip the video, and just follow these steps:
- Download the app by searching for Box.net (the Box.com address is still relatively new)
- Create an account (if you don’t have one)
- Login to activate a lifetime 50GB storage account.
Video. Below is a video that helps explain how to setup an account, how to reply to an invitation if you receive one, and how to download the app.