Think of the boat being in the center of the compass rose and the lines that go out are called "Bearings". So if you are instructed to hold on the 260 bearing at 21 miles, you should set up your HSI by putting the reciprocal of 260, 080 into the course line. This will result in the arrow pointing at the boat. You approach the holding point on a heading of 080 and when arriving at the 21 nm mark, begin a left turn to the outbound course of 280. Depending on your "Expect Approach Clearance" time, you manipulate your legs and turns so that you will arrive at the holding fix at exactly the time given. You are doing all of this at 250 kts. At the fix and at the time, you begin your descent at I don't remember what rate to 12 or 1500 feet then level off. I think you are right about turning to get on the final bearing at 15 miles but I can't say for certain. While heading down, I generally change my course indicator to reflect the final bearing.
A good rule of thumb is to think of Bearings as being FROM something and a COURSE is always TO something.