You may have seen those little clear glass christmas ornaments with impressed stars and other pretty shapes... it's done with fiber paper.
For mine, I use 3mm thick fiber paper (not sure what that is in inches!). The thicker the paper the more obvious the impression.
I cut the star, or tree, or heart, or other pretty shape out of the fiber paper, then put it on the primed kiln shelf with two layers of 3mm glass on the top and a little loop of wire between them to hang it from later. You could also add another loop at the bottom to hold beads or other decoration. You can obviously make your glass any shape - squares, rectangles, tree shapes, diamonds, circles, you name it!
You can use nichrome (high temperature) wire, or copper wire (which goes black but can be revived by soaking in a layer of tomato ketchup ... what is IN that stuff??!). I don't advise using galvanised wire as this gives off nasty fumes when you fire it. You could always drill a hole in your ornament instead, if you prefer.
If you decide you're going to use thinner glass (e.g. one sheet of 3mm) then you need to use more of a slump firing than a "full fuse" firing, as otherwise it can get really thin at the joins if you fire too long. Also you'll have to drill your holes rather than fusing your wire inside.
Once it has been fired, you'll find that the fiber has somewhat stuck to the bottom of your glass when you pick it up. Making sure you are wearing your breathing mask, I tend to dunk my ornaments in a pot of water and let them soak for a bit, then scrub off the fiber, then rinse. This way you can let the ceramic residue sink to the bottom of the pot and dispose of it properly (bag it and bin it) rather than letting it block up your sink trap.
To make your items 3D, you can slump them (if you want your design to stay nice and sharp then you need to slump gently) - It's not such a good idea to leave the fiber behind the glass when slumping as it can fall out! But if you're adding additional tack fused decoration to a flat piece then I'd leave the fiber behind the glass to help it hold the shape.
You can put more than one layer of fiber on if you want a more 3D effect, but be aware that higher piles of fiber can make the glass really thin if fused too long, so you'll need to do a bit of experimenting to make sure it holds well.
There are a range of fabulous free tutorials available on the web, including Bullseye Glass's fantastic kiln carving tutorial. Glass with a Past has one about kiln carving with bottle glass. Here's one with the basic process from Glass Fusing Made Easy and another one with some images for inspiration. Paul Tarlow has also written an ebook about it which you can buy.