Here's all you have to do:
here for a video that shows you how. Cut a piece of floss about 5 feet long to give you enough to work with.
IMPORTANT! Don't cut anything yet! Leave that tail as it is. You'll need the tail to wrap and secure everything.
Look! Now you can make a basic tassel. Yes, the above one is a bit wimpy looking, but you can use a lot more than 12 thread lengths in the tassel body. Also, try using different threads, like I did when I used the weird silk floss. And how about using a combination of colors in a single tassel? I made another one recently using Perle cotton. Love it!