Ok, so here is how the OEM Benelli sling mounts and operates
In the 1st pic, the circle shows strapping with the snaps is the loop to attach the sling to the front sling lug.
In the second pic, the slider is for snugging the weapon to the body when shooting a pistol or some other action where hands are off the gun.
In the third pic, there are two things going on. The red circle shows the rear sling attachment. The white circle shows the adjuster for the overall length of the sling.
The sling length should be adjusted with the white circled adjuster so the gun can be shouldered. Once this is done, it isn’t to be messed with. It is also adjusted to allow the snugging adjustment in the second pic to slide up to near the left armpit, for a right hand shooter, when snugging the gun
The straps at the clips allow for a quieter sling vs attaching the hooks directly to the gun, no metal on metal. The straps can be removed if one wishes to just use the clips.