system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] How do both sides know how to use the other sides weapons?

You would think that some random marine would have no idea how to use a plasma weapon with it being alien and all. I understand how Spartans know how to use them, they've been trained, but a random marine can use one with no problems? . Likewise, Elites would not only probably not know how to use a human weapon, but if I remember correctly, their code of honor forbids using human weapons, yet in all the times when Elites have been your allies, they can use human weapons just fine. Why is this?
gpt
The games are all set in the last few years of the war (or post-war). When you've been fighting an enemy for two and a half decades, you pick things up. 

In games where Elites are allies, they've realized that their whole religion is a scam. The whole code of honour doesn't apply anymore. Their human allies probably showed them how to use them.