I have used it for old cars and I have it (pictures).

You need to 1). find the timing mark; 2). clamp the aligater clamp (coil inside) on the first (check the manual) spark plug wire; 3). Aim the light of your gun to the mark; 4). Adjust the timing so that the timing light is exact falling in the mark. (I might be wrong in detail, since that was 20 or 30 years ago on my old Nissan, Datsun (former Nissan) and Toyota). If you need instruction I could send you the photo of the manual.