Using Unity and Forum Code

Hi all, I am new to coding in Unity and I had a few questions. I am making a game I plan on eventually selling.

1) The code that other members have posted on the forum; is it free to use or do I need permission from the user who posted it? 2) Is the code from the Unity Tutorials free from me to use when making my game (like the one they have for Unity 4 with the robots and stuff)?

I know the code would have to be open source or royalty free to use, but how do I know if it is one of those? I just want to avoid someone knocking down my door if I illegally used code. If neither of these are possible, I do know how to code in C++, so is C# too different from that?

Thanks in advance!