Note, I am not asking how to tie three different types of knots, but rather one knot that goes by three different names.
Its a knot that can be useful in building anchors especially at the top of fixed lines.
How one would tie this knot?
This one is almost identical to the figure eight on a bight, with one crucial difference.
When you get to the final step of the figure eight on a bight, instead of pushing the end of the bight through the loop you take another bight of the bight and push that through the loop, then flip the end of the first bight over the top.
Just like so,
Finally, if you were going to use this for an anchor you would clip one carabiner through each of the loops. This is also why some people refer to it as a bunny ears knot.
This knot works really well when fixing a rope to a two bolt anchor, and is easier to untie than a regular figure eight after being weighted.
The Double figure eight is tied like a figure eight on a bight, except instead of finishing the knot by pulling the bight through the loop, fold your bight into a second bight, pull the second bight part way through the loop, then loop the end of your first bight over the whole knot to finish it off.
One of the best resources online for learning how to tie knots is Animated Knots by Grog. Visit their site to watch step by step animations on how to tie knots.
You can watch a video tutorial on how to tie the Double Figure Eight on Grog's Youtube Channel as well.