Do I need to kill wildlife or something to get them or all three of them are active from start to finish? I tried to google it but with the release of stage 2 most of these guides seems outdated.
Playing non-tutorial games gets you Silver K at the end of the match. You use that to purchase perks. You left click on an available perk to assign it to the given slot. You right-click a perk to purchase it.
There are 3 different categories of perks, each gets applied to a respective slot. Each perk seems to have levels so you can purchase it multiple times. The slot 3 perks are more expensive than the slot 1 perks. If the perk is greyed out, like most of the ones in the screenshot, then they have yet to be purchased.
All of the perks that you assign to a slot are active for the entire match you are about to play.