"...explain exactly what it means..." You read it? It's pretty clear. The EU is making oppressive firearms laws(that were already that) for member countries. Looks like a complete list of everything the anti-firearm ownership mobs like the American Brady Campaign have been seeking. It's also got the amendments they made.
There's classifying firearms like AK's and M16icon's as "prohibited for civilian use" and "If converted into semi-automatic firearms, they should be classified in point 6 of category A." Plus mag capacity laws, storage laws, declaring that a firearm can be 'dangerous' all by itself all with no definitions of exactly what a Category A, B, or C firearm is.