Before you buy Indigo, make sure it's what you want. A blue chemical dye might better suit your needs. Before this sounds too negative, be assured that the blue obtained from Indigo is extraordinarily lovely and rewards you well for your effort. It is not water-soluble. It is a substantive dye, needing no mordant, yet the color achieved is extremely fast to washing and to light.
Indigo is one of the most ancient and revered of all dyestuffs.
The three recipes here all tell you how to dissolve Indigo, and how to dye with it. Deeper history and chemistry may be found in any good dye book. They should be treated with care and common sense, but without panic. Keep them dry, out of children's reach, away from food and use clean dry utensils for measuring. Wear rubber gloves, don't splash, especially keep out of eyes.