"Hackles" are the feathers around the neck. Here's a photo of a rooster with its hackles up:
With roosters, the hackles are long and thin. For instance, here's a rooster. He has hackle feathers around his neck, but if you look closely, you'll see they are far more magnificent, iridescent even, although they're not a spectacular color.
When roosters face off with an opponent, all their hackles will stand up in order to make themselves look larger and more intimidating. If you say something "got your hackles up," you mean that it got you ready to fight!
Sickles and the long, curling, showy feathers of the tail of a rooster.
This doesn't refer to ALL the tail feathers, only the ones on the sides with the curving shape of a sickle. You can see them above, the long ones hanging down. Hens don't have proper sickles in their tails. Their tails are shorter, and the tail feathers are generally straight.
Saddle feathers are the feathers in front of the tail. Both hens and roosters have saddles, but in a rooster the feathers are longer, softer, and pointier. Many fly tiers use saddle feathers to tie make lures with.
In the above photo, the saddle feathers are white and spill out on either side of the tail.