Roping is a technique used to achieve "slip" when conditioning your hair. This helps to prevent frizz and get curls to clump together nicely. Here is a quick rundown:
Section your hair into 4 or 5 sections. Working with one section at a time, apply an 5-10c amount of conditioner. Apply this conditioner in a downward motion, with your hands forming a circle like pictured
Using the inner curve where your thumb and finger meet, go hand over hand, as if your hair was a piece of rope you were pulling from your head downwards.
Wet your hands every so often and apply more water to the section you're working on. Next add a tiny amount more conditioner, then "rope" again. Continue to alternate between adding more water and more conditioner until you achieve the seaweed feeling.
This indicates that your hair is well moisturised and your cuticle layer is well sealed. Some Curlies find that using a special "wet Brush" or Denman brush before beginning "roping" helps to achieve the seaweed feeling more quickly.