Gather your supplies
Begin by cutting a small (1/4") slot in the center of one edge of the cardboard.
Make 2 more cuts, dividing each half into half again.
Then divide each of those sections in half again, and then again until you half small slits cut about 1/4" apart along both top and bottom edges. Doesn't have to be perfect, approximate is fine.
Take the end of the string and pull it into the first slot. Tape the tail of string flat against the cardboard on the backside.
Flip the cardboard over and pull string straight across to the first slit on the other side and around to the back.
Continue wrapping the string around the cardboard until all of the slits are full.
When you reach the end, bring the string to the back, cut and tape it to the cardboard. Now your loom is warped.
To begin weaving, choose a scrap of fabric and begin by weaving it over and under your strings, gently pulling it across.
Pull the fabric across, but leave a small tail at the end, taking care not to pull it through.
Now begin weaving back the other way, taking care to go UNDER the first warp string and working your way across to the end. Take care to be sure you're going OVER the strings you went UNDER last row.
When you reach the end of the fabric strip, leave the tail hanging out and being weaving a new strip across.
As you continue to weave, use your fingers to push the fabric up against the top of the loom, creating a "bunched" and tighter weaving.
Keep weaving, taking care not to pull too tightly against the warp -- this can create an "hourglass" shape. Towards the end, you can use something to help push the fabric through.
When you've filled the loom, it's time to cut it off the loom.
Next, use the scissors to trim the edges off the scraps. Don't worry about them - they'll tie in as you tighten the warp.
To cut your weaving off the loom, flip it over and begin cutting two strings at a time.
Bring those two strings around to the front and tie two half-hitch knots. Don't pull too tightly, just enough to hold the weaving together.
Continue cutting and tying all the way across the loom to the end. You might end up with three strings on one end and I'd that happens, just tie all three together.
Trim all the string ends and you're done!
These make great coasters (or mug rugs). Enjoy!