Because all of these PvP combats are being played on a different server, once you're a participant at a level, all of your levels and items will be left behind and you'll receive the normal set of RS Gold stats and get to pick a combat style that can boost certain stats. You can then choose a second combat style different from the first.
When the battles are finished after which you'll earn rank points and reward points when you win a match (1v1 battle or tournament) that the game arranges for you. While you will be able to organize duels and tournaments manually but these will not be rewarded with points.
In line with efforts to decrease RMT and improve the experience, any non-cosmetic rewards will only be usable in areas that allow PvP. You will not be able to attack anything but other players using them, either. Certain of these rewards are untradeable, where you'd expect them to be tradeable. This is a deliberate move so that they are less appealing to Buy RS Gold RMT spammers and scammers looking for products.