staking isn't new so i doubt you "came back from runescape" you would know what it is, its when you put in offers of money or items and fight to the death and the person who wins claims both of the offers.
Staking is pretty much just killing your opponent with whatever style combat you specify. I range box i did a couple a mil here and there. Once i was at a decent amount i staked it so it can go either way. Here is a pic of my most recent win. Edit: just saw your post about boxing didnt want to double post boxing is just no arming.