The monkey's fist is a decorative knot that can add some weight to the end of a rope, making it easier to throw. It can also act as a stopper if you need a stopper knot that large. It looks fairly complicated, and indeed, it took me several tries to get it right, but the turns are actually quite simple.
Step 1: Getting Started
I prefer to use my non-dominant hand to hold the rope so that my dominant hand can do the wraps. Start by holding the rope (or shoelace, whatever your case may be) like this. Make sure to leave a bit of space between your fingers for upcoming wraps. The less space you leave, the less slack you'll have in the knot when it comes time to tighten it, but less space makes it hard to do the second and third sets of wraps, so I recommend leaving your fingers as far apart as possible for your first knot.
Step 2: The First 3 Turns
Wrap the working end (the part of the rope that moves, in this case the long end away from the hand) around your index and middle fingers, going clockwise when staring down at the knot. Start next to the standing end (the end of the rope that isn't the working end), and work your way to your fingertips until you have completed 3 wraps.
Step 3: Setting Up the Next 3 Wraps
Take the working end and feed it through the middle of the first 3 wraps. Start by taking it where it wound up after the first 3 wraps and going down through the middle and out the back (image 1). Bring the working end back around to the front to set up the working end for the second set of wraps (image 2).
Step 4: The Second Set of Wraps
Start this set of wraps by taking the working end and passing it to the back between your fingers and under everything. That should complete your first wrap. Do the same thing two more times, placing each wrap farther away from you than the one before it. This keeps the first set of 3 wraps in place. Now, to set up the working end for the third and final set of 3 wraps, leave it behind the knot and leading away from you.
Step 5: Setting Up the Final Wraps
This part can be a bit tricky, so it gets its own step. Remove your fingers from the knot. It should be fairly stable now and not untie itself. You should have two loops, separated by the second set of 3 wraps. Assuming the standing end is pointing at you, one loop should be close to you and the other farther away. Take the working end from the previous step and bring it up through the farther loop. That will set up the final set of wraps.
Step 6: The Last 3 Wraps
Now that you have the final 3 wraps set up, take the working end and wrap the second set of 3 wraps, going down into the close loop and up and out of the farther loop. In this case, make your first wrap as far to the right as possible, and work your way left with each sequential wrap. Make sure you get each wrap outside the second set of wraps but inside the first set. This will cause set 2 to secure set 1, set 3 to secure set 2, and set 1 to secure set 3. Once this set of wraps is done, the knot is almost finished, but there's one more thing to take care of before working the knot into shape.
Step 7: Hiding the Standing End
This whole time, the standing end has just been sitting there, pointing at you and not looking very pretty. It's time to hide it. Tie an overhand knot at the end of the standing end and tuck it into the middle of all the wraps. Once that's done, you shouldn't be able to tell where the rope ends and it should just look like a series of 3 wraps all securing each other. Now the knot is ready for tightening.
Step 8: Tightening the Knot
After tucking the standing end into the middle of all the wraps, you're left with a loose bunch of wraps that don't look like much more than perhaps a rat's nest. To get that characteristic spherical shape of the monkey's fist, we have to tighten the knot. This can take a while and will likely test your patience, but the final result is quite satisfying indeed. Tug on the working end and locate the wrap it connects to. Follow that wrap and tug on it. Keep following each wrap through the knot until you reach the standing end inside the core. Repeat that series of steps until all the slack has been removed. Each iteration "moves" all the slack one wrap closer to the working end. It's not uncommon to wind up with a scenario like in image 1, where the slack is concentrated on 2 or 3 different wraps. Just keep iterating through these steps and you'll eventually work it all out of the knot. Once it's all within one or two wraps of the working end, just pull on the working end to remove all the slack from the knot, finally giving you a true monkey's fist.