How do you make glass?

I cant get glass that can be shattered! How do I do that?

[Ding Bat]

When you make your window frame, in 3D mode, point at the wall just below the window and hit the 'm' key, that masks the wall. You'll see the ugly brown bricks appear.
Then put the cursor on the brown brick and change the texture to the glass #503.
Then hit the 'b' & 'h' keys. The 'b' is blocking and the 'h' makes it breakable.