What Proof of Work does IOTA use? I have some trouble finding valid information about IOTA. Actually I would be nice if there would be a good source. 

So my question is: 
Bitcoin uses the SHA-256 twice and some "target bits" for hashing it's blocks. 

What PoW does IOTA use? Some sort of Hashcash Lite - but how does this work in detail?
Is there also a header with a timestamp and some previous block hash?
IOTA doesn't use proof of work.
IOTA is a tangle, and the consensus is reach based on the information propagation in the network. You can find more information about it here:
https://forum.iota.org/t/iota-consensus-masterclass/1193