KDA, Slayer, and Warzone

Ok, so I have a question for everyone.

When I go to my service record and highlight Arena, it gives me two different stats, KDA and Slayer. What are the differences between the two? Also, there’s one more registered game in KDA than there is in Slayer. What is that about?

I understand the objective in Warzone, but do kills in Warzone contribute to these stats as well? If not, then do kills not even matter in Warzone at all? Is it basically capture points, and it doesn’t matter how many times you kill the enemy team or die?

Thanks for taking the time to answer these questions, and helping me to better understand the game!