I've seen diagrams with brief explanations in the Benelli advertisements many times. However, I probably don't remember it well enough to describe it here. Try the Benelli website.
Ah, what the heck. I'll take a stab at it from memory. If I'm wrong, I'm sure that someone will be along shortly to correct me. When you fire a round, the gun recoils. The rearward movement of the gun causes a coil spring in the bolt to compress due to the "inertia" of the bolt resisting the rearward movement. Then the bolt unlocks and moves rearward in relation to the receiver due to the stored energy in the compressed spring. This causes the empty shell to be ejected. The hammer is also cocked on the way back. Then the spring in the bolt compresses again (due to the inertia of the moving bolt) when it hits the end of it's travel (near the rear of receiver). This compressed spring provides the stored energy to return the bolt forward, picking up the new round on it's way.
How's that? Hopefully I'm right, but even if I'm wrong, I should get an "A" for creative writing, right?