brace magic - yes it exists, but it is worth a little reading, practice and work on yourself otherwise a brace on a string would work the same way, and the best is just to join the circle of people engaged in esotericism

The color of the string is indeed important, as in candle magic. Green for health, red for love, etc. Write down your intention on a piece of paper, preferably in the form of a short rhyme. By tying more knots, you say the intention. I usually do seven knots and seven intentions.