"Thank you very much for the info! So, is this like free for all (player with higest points win) or/and team deathmatch (team with highest points win)? Or can the Swat mode be applied to any other game mode as well?"
SWAT is Team Deathmatch. Usually 4v4, first team to 50 kills wins. SWAT is generally kept to just this, right Arachny?
As for your other question. Power Weapons (Missile Launcher, Fuel Rod, Spartan Laser, Sniper... etc) in Warzone can be obtained via the use of REQ Cards. These are available to purchase with real money, or using the in-game 'REQ Points.' You use one card for one weapon.
Eg. I use a REQ card for a Sniper Rifle, and so now I spawn with a Sniper. It can be a bit confusing at first, but you will get used to it! I would suggest trying to find a video to watch of this in action.
In Arena there are weapon pickups around the map. Power Weapons have a timer so both teams can battle it out over the control of a spawning missile launcher. It's great fun.