Required; One 10mtr (roughly 45 ft) length of rope, one keychain ring.
Lock one end of the rope in the ring, then loop the other end through.
pull it roughly 15 foot through, leaving the other end in a 30 foot loop; you'll have folded the rope in thirds..
Take the long loop of rope in your hand just below the key ring. Then, put the short end of the rope through the key ring ten times, wrapping around your hand (protip - alternate which 'sides' of the long loop you pass) - ten or so times, leaving some slack and creating a loose handle consisting of ten-or-so loose, small loops.
Wrap the short end once behind the ring and loop it on itself to begin the wrap for the handle...
... then wrap the short end -tightly- around the handle to finish it. The tighter the better; this and how close you can get to the -end- of the handle determine the amount of control you'll have over the finished flogger.
Once you reach the end of the handle, tie off the short end on itself and keep it out of the way. Be sure to leave some room before the handle's loops.
To form the falls of the flogger, thread the long loop though the remaining loops at the bottom of your handle, leaving a length behind each time...
... Which will take some fiddling, but eventually will result in a number of tails of equal length. Use the short end that you've kept apart previously, to tie these in place. Protip - by wrapping the falls that you form around something you can adjust their length and the amount of falls that you make more easilly. On this flogger, the more falls you form, the more it will 'thud' versus 'sting' - but the shorter the falls will be. I usually keep them at roughly a foot and a half to two foot long, depending on purpose.
Until you cut the tails open, you can still take this flogger apart into rope and ring. Choose wisely, young padawan.

If you cut the tails, it's advisable to glue or otherwise lock the tails at the handle, since there's nothing really holding them in the handle but the tight wrap of short end. (You did that TIGHTLY, right?)