From Dust Game Guide

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                               ||  Story Mode  ||                          [S0]
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Before we get started, I'd like to note that there are a ton of ways to 
complete each level. This guide is simply how I've done it.

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                                 | The Breath |                            [S1]
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                                 | ========== |

This first level is a basic tutorial mission. There are no real dangers here,
and you can play around with what little earth it gives you.

Hold the Left Trigger down to create the Breath. You will control this 
throughout the game. When prompted, use the Left Thumbstick to move and the
Right Thumbstick to look around. Your people are already moving towards the 
goal, as indicated by the white lines laying on the ground. You can press the
Right Bumper to zoom out and get a better look at the area. Follow the men
until they can go no further. The white lines turn red, and they'll start 
chattering for help. You need to make a bridge of earth that allows them to 
get over to the portal.

The light brown material scattered across the area is earth. The black 
material is rock. You cannot alter it at this point. You can, however, pick
up the earth and deposit it elsewhere. Hold the Left Trigger down to scoop up
a bunch of earth. When you've gotten all you can carry, you'll hear a sound 
effect and your controller will vibrate a bit. Now move your ball of earth 
to the people and start laying it down in a line that extends from them to the
opposite shore. You'll have to do this at least a couple of times to make a 
complete bridge. Once they're able to get across, the people will automatically
gather at the portal. After five men gather at the portal, you can press A to
continue to the next level.

Before you do that, I suggest playing around the earth a bit, to see how it 
interacts with the world. If you're carrying around earth (or anything, for 
that matter), you can empty it all out at once by holding the Right Trigger 
and pressing the Left Trigger.