I can already connect my conversation to my Facebook page and the bot is working. My Problem is that i couldn\'t find a single tutorial on how to make calls to a server that is
You need to develop an orchestrating application, that would be responsible to connect the IBM Watson Conversation with your desired Fronted, Facebook in this case, and the Backend systems. I imagine that you are using the automatic deploy to Facebook from the Conversation Tooling, this option would not resolve your need to access a Backend.
The image passed by @data_henrik shows exactly that.
In conversation, you can create context variables that will be used as triggers in the Orchestrator to let him know when you need to call a Backend service to provide an information and then write the response into the Conversation context.
About using the Chatbot to login into a system, passing a password, this isn't a safe option since all information typed would go to Watson Conversation log and any person with access to the tooling/api could see the passwords.