Not sure how you do it on a firearm but staking is the process of compressing metal with a stake tool. The metal will swell in the ends resulting in a tight fit that wont work loose. I worked previously at an valve train manufacturing plant and we staked the axles in the Rollers to assure that they didn't work loose.
This picture doesn't show the actual stake mark. But the needle bearings would be inserted in the roller the roller would the be placed in the lifter the axel would be pushed in the lifter between the bearing and staked. The stake would make the axel swell against the lifter walls and it wouldn't fall out.
In the context of that thread I assume that its the same concept only with a gun and not automotive parts.
Sorry if this is confusing ....its hard to explain in text format lol