well to start im not the right person to help you, but i will try it somehow.
1- To start with => WriteProcessMemory(), ReadProcessMemory(), OpenProcess(), GetWindowThreadProcessId(), if you already know the basics you could start by looking a bit for these functions. have a look in here: Process and Thread Functions
2- You actually don't directly hack those passwords and etc with a language... (unless you are a pro hacker, and you manage to get access to facebook server DB's, and get the passwords, etc..etc..etc..) you would make a key-logger, or something, trick people and steal their password. A Language... well any language is fine to make a key-logger, if you actually feel good using it. (By the way, thats illegal here on MPGH)
3- If it was easy everyone would be able to do it and how funny is that..?