Halo 5's unlock system operates via REQ packs - digital cards that grant access to weapons, armor, and more. When the game comes out on October 27, you'll be able to buy them with in-game or real-world money. But right now, today, you can unlock your first REQ pack by watching a series of 10 videos in which protagonists Chief and Locke tell you what it means to be a space-faring supersoldier of the future.
In case your freemium senses were tingling: yes, it does sound a lot like how certain games (particularly those on mobile) will provide in-game rewards for watching an advertisement. The nice thing is, in this case, the videos are extremely short - around 10 seconds each - and they're actually interesting to watch. You'll get to learn more about what drives Chief and his pursuer while catching glimpses of new game footage. For about a minute's worth of trouble, you'll earn the Vengeance Assault Rifle skin.
Sounds good to me. After all, as the great philosopher John-117 once said, "I need a weapon (skin)."