You can find a couple of tutorials here and here, but basically you just cut strips of fabric (vary the length and width according to the look you want) and tie them onto either twine or a strand of lights. You'll notice that one of these links was a birthday garland and the other was for a patriotic themed Christmas tree. The possibilities really are endless.
Here's the first one I did years ago during a Relief Society craft night. It was too long ago to remember how much fabric I needed, so sorry about that, but it is a great way to use up scraps. For this project we also painted wooden stocking shapes and added them to the garland.
"girls' night" at Thanksgiving. Isn't it amazing how different they look for being essentially the same project?
What are some of your favorite simple crafting decorating projects? (Hmm, do I need some commas in there?)