Bitcoin runs Proof of work. You "mine" a block by solving a hash. LOTS of power needed to make the network secure.
Proof of Stake: Every coin has a chance to "mine" the next block. Power needed? Basically the verification of that mining, nothing artificially hard to do. Thats why you can do this verification on low-power computers. Every smartphone can do that.
one could say that the cost of proof of work adds physical value to the coin, while proof of stake the value is 100% speculative
ah ok, thanks