Choose the yarn you'll be using for this project and some appropriately sized needles. If you're using fingering weight yarn I recommend using 3.75 mm needles, or if you're using DK weight yarn I recommend using 4.5 mm needles.
Before you start knitting you'll need to calculate how long your I-cord needs to be. Measure your wrist and decide how many times you'd like the I-cord to wrap around your wrist. Multiply your wrist measurement by the number of wraps, then add at least an additional 0.5" or 1.3 cm to this number to ensure your bracelet isn't too tight. The formula for this is:
(Wrist measurement × number of wraps) + additional ease = I-cord length
Make a note of the resulting number as this is how long your I-cord will need to be.
Cast on three stitches, ensuring you leave a tail which is at least 6" / 15 cm long. You can use any cast on method you like for this as it's only a small number of stitches, I used the long tail cast on.
Once you've cast on your stitches do not turn your work. Instead you need to slip the three stitches purlwise onto your left needle. The working yarn should be at the left end of your stitches, so it will reach across the back of your stitches when you start knitting.
Knit the three stitches, then slip them purlwise back onto your left needle. Repeat this until the I-cord is the length you calculated in step two.