CRED
You can earn CRED by completing gigs, taking part in events and increasing your Rep level. You also get a small amount of CRED just for finishing a match and winning matches. Spend CRED to purchase HDDs (Haul Disk Drops) at the Broker.
HDD
Each HDD will contain a weapon skin and/or visual upgrade (kill counter). You'll be able to see a preview of the potential rewards from a HDD when you select it. The items will have different rarity levels: Rare, Epic and Legendary.
There are no duplicates until you have opened up all items from an HDD. Once you have unlocked all items from a HDD, any future HDD openings will award CRED instead of a cosmetic item.
Legendary weapon skins opened from an HDD will also come serialized so the first player in the world to open one will get #1, the next gets #2 and so on. To see the specific HDD drop odds and rarity guarantees select Details when you are viewing a HDD.