Unreal Multiplayer only in Blueprint ?

Hey,

Do i have to use blueprint in order to use the multiplayer network stuff from unreal 4?
Or is there a way that i can use the network stuff in c++ too ?
And if yes. Are there some tutorials or documentation for the network api ?

No.

By nature, every single Blueprint function has a corresponding C++ implementation. Just do search the codebase for the blueprint function you want to use, and you’ll have the C++ function. The blueprint name might sometimes be disguised with a DisplayName metadata, so you might have to search with or without spaces, depending.

So between what tutorials and documentation are available for blueprint, and the actual source code, you should be covered on that front.