Assumed somebody knows one of my several addresses in my wallet for receiving bitcoins, can he link this address with the other addresses I got? Or does every address stand for its own?
Say you have two addresses, address A and address B. If someone sends coins to you at address A, and someone also sends coins to address B, then no one can link those addresses together. They are just separate transactions with separate transaction outputs, just like any two transactions that are sent to different people.
But now, if you have to send some coins and you need to spend both of the previous transaction outputs were generated by sending to address A and address B, then you will be associating those addresses together. This is not a proven association, two different people could come together and spend two of their outputs together in the same transaction, but this is not a very likely scenario. The more likely scenario is that the person who initiated that transaction (you) owns both address A and address B.
That said, just because someone watching the block chain can tell that the SAME person owns address A and address B, that doesn't mean that they know that YOU are the one who owns address A and address B. Read this stack exchange for more info: How anonymous are Bitcoin transactions?. If they know that you are the owner of address A, though, then they would be able to determine that you are (likely) also the owner of address B (but only if you have made a transaction before that spends from both of those addresses).