create .dll file from a c++ code. VS 2013

[amirrezadll]

Hi
I'm going to create a .dll file from a code . I'm beginner in C++ , So I followed a youtube video step by step but I'm getting following error:
fatal error LNK1120: 3 unresolved externals
I'm beginner in VS so please simply tell me what should I do
Thank you

[Nico]

Please post the source-code from your DLL, the interface header from the DLL and the source-code of the program that you made to call the functions in your DLL.

Without this information I don't think there is a way to help you.