How do perk decks work?

I dont' understand how this even works? It just got updated so there's no more set bonuses. Can someone explain the full concept to me?

First, you get perk points by gaining experience, you can then pick a perk deck to put your perk points into. The amount of perk points required to unlock a perk in the perk deck goes up the further you get into the deck.

Perks will give you bonuses similar to the old tier bonuses, but also some more interesting ones, such as the ability to buy an asset that allows you to switch armour while in the game.

You can refund your points and pick another deck to put them into as long as you have not fully unlocked the perk you're refunding the points from. Once a perk is unlocked, those points have been spent.

And finally you can only have a single perk deck active at a time, but you can invest in many.