You’ll need plain white cotton cloth, either just pieces of cloth or white T-shirts (but make sure they are 100 percent cotton!), and dye – the most commonly used kind is RIT dye. Follow the instructions on the RIT dye to make up the dye. Add a couple of spoonfuls of vinegar. Then take the cloth and fold it in patterns (or at random), tying it tightly with kitchen string or rubber bands all over.
The more tying you do, the more complex the pattern will be. Make sure the tying is very tight, so the dye can’t get under it.
When your cloth is tightly tied in many places, dip it in the dye according to the directions. If you are going to dye your cloth more than one color, do the lightest color first (usually yellow).
Here’s an old video with instructions.
Then untie your cloth, and retie it in a different pattern, and dye it again (if you want more than one color).
When you are done, rinse the cloth in cold water. Then you only need to hang the cloth up to dry. Make sure to fix the dye according to the directions, before you wash it, or the dye will run.