War Games refer to a collection of game types in Halo 4 in which you play competitively against other human players. These battles are training simulations performed by Spartan IVs onboard the infinity, which they use to improve their abilities for Spartan Ops. There are no computer controlled enemies in War Games; every single ally and enemy is a real human player.
War Games offers an interesting dynamic to Halo 4 quite different from either the Campaign or Spartan Ops. Because you are playing against real players, you get an opportunity to fight enemies much more intelligent than those in the Campaign or Spartan Ops. Therefore, some of the strategies that I provide for the Campaign do not work nearly as well in War Games. There is no single “best” strategy, so experiment with many different tactics and choose one that best fits your strengths and play style.
In War Games and Spartan Ops, you receive experience after completing each game. This experience is used to level up your Spartan IV character. As you level up, you unlock new equipment (such as weapons, armor abilities, and perks) and new armor. Each level requires more experience to unlock, so you will level up quickly at first and slowly later on. After you reach level 20, you will have unlocked all equipment, and any levels past that will have little effect on your gameplay.
There are 3 ways to gain experience. The primary way is to complete games in either War Games or Spartan Ops. After each game, you will be rewarded a fixed completion bonus and a much smaller bonus based on your success during that game. In general, you will receive around 2500 experience from shorter games (slayer, oddball, etc.) and 3000 experience from longer games (Spartan Ops, Big Team Battle, CTF). The second way to gain experience is by completing challenges. There are an assortment of War Games, Campaign, and Spartan Ops challenges that you can complete to gain extra experience, with rewards ranging from 1000 to 20,000 experience depending on the difficulty of the challenge.