Edit, I type slow lol.
Okay let's simplify.
There are two basic types of hop currently available.
The traditional type (a rubber and a nub) and then the R hop type (those will have a patch cut to fill the hop window)
Let's get deeper. The traditional hop has come a long way, now one has a lot of choices for rubbers and nubs. I'm sure we all know the standard, a rubber with a mound of some sort on it, then a small bit of rubber (nub) that the hop arm uses to push on the rubber pushing the mound into the barrel.
Now we have the "flat hop" types of rubbers, they have no mound inside, they require a larger nub to push the rubber into the hop window.
This allows us to create many shapes and sizes to try and achieve better hop. The two standards are the flat hop and the bridge hop. Flat being exactly that, a flat or gently curved nub that is (hopefully) sized to just fit into the hop window. Bridge having a notch of some sort in the middle, to apply the hop more to the sides of the bb to help center it.
Now the rhop will use some sort of nub, usually a flat one from my understanding, a lot of times a custom cut (home made from eraser or something) then a custom/semi custom (depending on the kit and barrel used) rubber is cut to fit the hop window, then it is glued to the barrel and sanded smooth then either a modified rubber or just a pre made smooth one and the above mentioned custom fit nub are combined.
The goal of both this and the flat/bridge methods is to provide more hop by having a larger contact area for the bb to aquire spin, at the same time this reduces the ammount of hop needed to generate lift.
Don't miss understand, you will need to apply the same amount of spin to lift a given weight at a given velocity, but you will be able to provide spin with less effort, (ie less pressure from the hop up causing loss of fps and potential bouncing in barrel from starting off pushed down to the bottom etc..)
This in turn means heavier rounds could potentially be fired I creasing effective range.
I'm sure some of the methods could be gone into more detail and I didn't touch on ones I haven't heard of or used at least once lol.
here is a bridge style.
A flat hop, note the modify is a little small to fill the window using most inners and most hop units, the above prometheus has a chart to trim for different guns.
Some assorted attempts at making the traditional hop more effective with some rhop pads to the left.
And the makings of an rhop install.
credit to the owners of the pics, just for your reference.
Also it should be noted the best bang out of an rhop comes from first widening the window on the barrel so you can fit the biggest patch possible, some moving of the hop units window may also be needed. That being said good results can come from fitting to the stock window, however I found that the prometheus rubber with the bridge tensioner (as they call it) works just as well.