At the top of your screen are a play, pause, and fast forward button. Press the Play button now!
Walk around using the arrow keys, and move your head using the mouse. Check that out for instant gratification!
Tip
Fall through the floor
If the only jaw that dropped was that of your game character falling through the floor, then go back to your character controller (the capsule thing) and move it up higher above the terrain. Now also check you've checked the generate colliders box in the FBXImporter tab when you select the terrain, as described earlier. Colliders describe which geometry is solid so that your character doesn't move through it.
Use the Spacebar to jump, too. You should have a first person view like the one above.
When you're done looking around your magnificent creation, click on the Play button again to return to the editor.
Wowsers! Was it really that simple? Yep. Now, check the following.