As the name implies, it's just a simple band. It doesn't have a cap or require any easing. It's wider at the shoulder and then tapers to very narrow underneath the arm.
Here's how you do it. Measure your front and back armholes, excluding the seam allowances. (Double click pictures to see the text better.)
Sew your sleeve in as usual, but don't worry about easing, as it should fit exactly. Match your circle up to your shoulder seam. I finished the raw edge with my serger to keep it very neat.