Could someone agree me, so i can make sure i understood dPOW.
It is like a normal POW-System, like BTC, but additionally it goes through the 64 notary-nodes and has to be accepted from each of them?
And another noobish question: Does it somehow decrease the speed of the blockchain?
Not exactly. the 64 nodes provide an optional security overlay.
dPoW is consensus mechanism agnostic, the underlying can be PoW, PoS, etc.
KMD uses equihash as its PoW
Fundamentally it can run just with this PoW, at one minute blocks.
Additionally, there are 64 notary nodes that were elected by the KMD stakeholders that have special privileges. These nodes are able to mine at an easy difficulty, but only one block every 65. The rest of the time they are at normal difficulty.
In exchange for this right to mine at a low cost (profits), the notary nodes must run a high capacity server and generate notarization transactions. These transactions are added to the normal set of transactions and mined as a standard transaction. They are similar to a multisig, but since there are 64 nodes, it is a custom form of transaction. The same transaction is made on the BTC blockchain
The consensus code uses these notarizations to know what blocks have been notarized and once notarized they cannot be rewritten.
Notice, if the notary nodes disappeared, things work normally, just without the additional layer of security. Additionally the GPU miners and the notary miners are competing for the same blocks and this division makes any attempt at rewriting the chain a lot more challenging, since no matter how much hashpower you have to attack, the notary nodes will not need any additional hashpower.
In other words, it is not possible to get more than 51% effective hashrate with notary nodes mining as the notary node's effective hash power increases with the overall hashrate. If nobody can obtain 51% of hashpower, then nobody can do a 51% attack.
This means it will be much harder to make a successful attack and the window of time to conduct any attack closes as soon as a notarization happens. (unless you are also able to simultaneously rewrite the BTC chain)
dPoW can be chained. Since we have the KMD chain already paying the crazy expensive BTC fees, there is no need for another chain to do this to obtain the BTC security. The KMD assetchains take advantage of this and they notarize to the KMD chain, knowing that KMD will be notarized to BTC.
So without much hashrate at all, dozens of assetchains are all benefiting from BTC level security. There is no reason there cant be thousands of chains all using KMD dPoW to obtain the same. For the cost of KMD you can get BTC level security.