So, every 5s and 6s I get, I do the full damage of the weapon? Or it means if the attacks success, I do the normal amount of damage for each one of them?
Uhh, both. It's resolved as a multiple attacks, each with a fraction of the normal dice pool, but each doing full damage.
Suppose
Alan is going H.A.M. at some goons with his SMG in full-auto mode. Alan has 20 dice for Firearms (Automatics). The gun does DV 6P. Let's say he's in a target-rich environment and there are 10 (!) goons to choose from.
Alan could attack two goons with half his dice each. Resolve each attack normally, but Alan only rolls 10 dice to attack. Say Alan rolls 3 hits and the first goon gets 1 hit on his defence test. That goon now soaks 8P damage (6P for the gun plus 2 for Alan's net hit.) Then Alan attacks the second goon, rolling 1 hit; the goon rolls 2 hits, so the second hit misses.
(Aside: a common speedup trick some GMs do here is only make Alan roll his 10 dice once, and use the number of hits from that roll against all the goons in turn. It's just to make resolution go a little faster so Alan isn't spending forever rolling dice and slowing the table down. In that case, Alan's 3 hits on the first roll would have applied to the second goon, who would have been hit. Also note I've ignored comparing Attack Rating and Defence Rating for Edge above, just to make the text shorter, but you would do that for each attack in turn.)If Alan was feeling lucky, he could go further. Say he shoots at 5 goons, each of them with just 4 dice. Obviously there's a good chance he's going to miss a lot now but if his dice are hot, who knows? Any hit he lands is doing 6P, so even without a lot of net hits from his attack test he's laying down a lot of damage. He might just blow a load of them away. Dakka dakka dakka!