validators stake a portion of their Ethers as stake.
validators start validating the blocks. when they discover a block which they think can be added to the chain, they will validate it by placing a bet on it.
If the block gets appended, he validators will get a reward proportionate to their bets.
Malicious validator acts trying to do a “nothing at stake”, the will immediately be punished, and all of their stake is going to get slashed.
all Pros of Proof of stake
punish validator trying to do a “nothing at stake” attack,
punishing miners who go offline, unintentionally or not,
Casper the Friendly Finality Gadget (FFG), hybrid PoW/PoS that will be implmented first and ease transtion to full PoS. blocks are mined using POW, every 50th block a POS checkpoint where finality is assessed by a network of validators will be used.
Casper the Friendly GHOST: Correct-by-Construction (CBC): full PoS