In Minecraft, you can make Glass cubes which you can use for decoration, or simply as a safe window for your house.
To make glass, you’ll need a Furnace. Place a block of Sand in the top, and any heat source in the bottom, like a piece of wood, coal, or charcoal. You’ll get one cube of glass for every cube of sand you use.
Once you place a glass block, you can’t get it back. Once you break it, it’s gone for good.