Something I often see new comers to fly tying struggle with (myself included a few years ago) is hackle. It seems like such a complex subject, but it really isn't. Especially with the choice of genetic hackle we now have. To help demystify this topic, I think it's best to break it down into bite size chunks.
Firstly, simply put, there's male and female chickens, cock and hen. Hen fibres are softer and often tied on wet flies. Cock hackle fibres on the other hand are stiffer and before genetic hackle (I'll get to this in a bit) was on offer, tyers would use cock hackle available at the time and add more wraps or double the feathers up to help increase the barbs. After all, these barbs are what holds the fly on the surface.
In modern day tying however, genetic (specially bred birds) offer way more and stiffer barbs than the cheaper options you can find (Chinese, Indian or domestic). As a whole, genetic hackle will offer better, longer feathers and excellent value for money. This also applies to genetic hen hackle, albeit they are still aimed at wet flies as the barbs are softer than that of a male chicken. So, at this point, an easy way to remember it is that genetic cock (male) birds are best suited to dry flies, the rest, well the opposite and are better suited to dressing wet flies.
Capes on the other hand are from the neck area (imagine where a cape would be up around the shoulders) and has a vast range of different sizes available. This could be feathers for micro flies (size 20 hooks and smaller) all the way to much larger feathers for wet fly bodies or tailing fibres etc. So the main difference between them, saddles offer a lot of similar sizes for tying a lot of the same size flies (often 12/14s in cock saddles) or a variety of feathers from a cape for different sized flies.