Creating a Scene

The first step in building any new document is to create the scenes that you want to display (in either 2D or 3D).
To add a scene, find the Scenes window (by default in the bottom right), and press the Add Scene button.
In the Add New Scene dialog that appears press Create a new 3D scene.

Adding a Mesh

Great! Now we're going to add something interesting to the scene.
In this example, we'll add a simple chessboard. To do this, find the Meshes window (by default in the bottom right) and click the Add Mesh button.
From the Add New Mesh dialog, find and select the chessboard mesh (note by hovering over a mesh you get a quick thumbnail and description).

Preview

We now have an object in a scene - hit F12 to preview this.

You can navigate a preview with W,S,A,D and by right clicking and dragging the mouse.
When you've finished with the preview, close the window or press Escape.
The object is great, but it doesn't really do anything yet. To make it more interesting, we'll add some script to it.
First, we'll add a sound to play to the scene. Find the Sounds window (bottom left by default, with a musical note symbol on the tab).
Click the Add Sound button and in the Add New Sound window, select the metalclang.

Adding Script

OK, now it's time to add the script.
Select the chessboard with a left click, then right click it and choose Edit Script from the popup menu.
In the script editor double click 'onClick' (top right).
Click the mouse in the source code editor inside the curly braces, and type:-

sounds.metalclang.play();

Note that as you type, a help window pops up to give you a list of all the sounds currently in the scene.
Save the script into the object by choosing the Save option from the File menu (or by pressing CTRL+S).