So what has the picture got to do with rainy day activities? These are shells from clams that were devoured by a Lewis' moon snail (Euspira lewisii). The shells wash up on to the shore after winter storms. With their perfect holes they just cry out to be strung onto some cord.
First, you need to measure off yarn as if you were making a warp. Make the "warp" about 3 times longer than you want for a finished cord. The number of threads will depend upon how thick your yarn is and how thick you want the final cord. You will need to do a sample. Tie a knot in each end of the finished warp. One knot goes over the cup hook while your friend holds the other under light tension. Allow the drill to twist the yarn until it is close to the point of "kinking" (again sample) then without losing the tension take the knot your friend is holding and slip it onto the cuphook. Now, reverse the drill and ply the doubled cord until it is firm enough. Again, without losing the tension, knot the cord to hold the twist. Now congratulate yourself you are finished.
Back to those poor clams. Our group is putting together the registration and goodie bags for the Retreat that will take place at the end of March so last week we got together and made shell necklaces for the goodie bags. We set up a production line. Pat warped, Karen whirled and Wendy threaded cord through holes. Eh voila, we have necklaces!
One final tip. Before you cut the cord, wrap the cutting area firmly with tape then cut in the middle of the taped area. This will hold the twist and stiffen the end so that you can poke it through a hole. Tie a knot to hold the twist permanently after you have finished stringing items onto the cord.