There was no mention of what the purpose was or what assembler or compiler is used, so it doesn't make sense to give out links to random tutorials if we don't know half the details. Some assembly languages have built-in syntax for setting the calling convention, some don't. Some compilers need specially named functions in the object files, some don't. Some development environments have specific ways to set the link dependencies in an IDE, others use the command line. If DLLs are used, then an entirely different approach would be needed.
Linking c++ to assembly is a relatively advanced thing to do, you can't expect easy solutions where one size fits all. A general question was asked, a general answer was given. If you need more information, then we'll be happy to give it. Just ask, give more details and we'll guide a person to the right path. That's how a forum works.
I hope this was a good enough explanation.