When you first use High Fidelity, your experience is determined by whether or not you're wearing a Head Mounted Display (HMD).
If you are wearing an HMD, you will see your Sandbox first. Your Sandbox is your own space where you can create content, host events and hang out with your friends.
If you're in Desktop Mode, you will enter High Fidelity's Tutorial. This domain is a first-time user experience where you will learn how to move, grab items, choose your avatar, navigate your menus, enable your privacy bubble, and travel between domains.