Making a simple loom is intriguing, but making a simple loom out of cardboard is resourceful. The loom consists of parts that can be found for free (or bought for very little money.)
Cut out the loom from a piece of cardboard that is 8 1/2 by 11 inches. Orient the cardboard like you would a sheet of notebook paper (the same size.) Make a cut in the cardboard that extends 6 inches side to side, centered across the 8-1/2 inch width. The slit should also be 5 1/2 inches for the top and bottom edges of the cardboard.
Make a 1 inch slit at a 90 degree angle from the original slit at each end. These slits need to go towards the same end of the cardboard. At the ends of the two side slits, make a shallow slit from one to another where this new flap is to be "hinged." Push on the side of the flap that has the cut to bend the flap.
Cut thirteen 1 inch sections of coffee straws. Into the open end of the flap, insert them into every third hole of the corrugation exposed in the edge. Do not insert the straw far enough to interfere with the hinge.
Make the slits 1/4 inch deep starting at the two far ends at each of the thirteen locations the straws point at when the flap is moved towards that end's direction. Make a second series of cuts, just as deep, located between each of the thirteen cuts at each end. Bend one of the slit ends up, 1 inch below the edge.
Cut the "shuttle" (the part that you pass side to side) from the paint stir stick by tracing the outline with your knife. Make it a 1 inch wide and 7 inch long rectangle. Saw the wood with your serrated knife. Cut a bowl-shaped groove in either end. Sand the corners smooth and round them by rubbing the stick on the sidewalk.
Set up the loom by slipping the end of a 135 inch section of string between the "toes" into the slits at one corner of the loom. Slip the string through the straw (in at the cardboard flap's hinge, then out the other side) and around the "toe" so that it enters and then emerges out of the two neighboring slits at the corner directly across from where you tied the yarn to start. Run the string the opposite way without passing through a straw and repeat the procedure going back and forth but only going through the straw at every other pass (this is the reason that only some of the slits were lined up with the straws.) Tie off the string when you get to the end. To "shift" the string, move the flap either up or down before each shuttle pass. You can use tape to reinforce the hinge of the flap.
Be careful with sharp objects and moving parts. Cut away from yourself. Use a suitable backing under the cardboard when you cut.